Here's my list of the best cards in the set so far. These are cards that should be good for any strategy- look to these cards to keep in your deck, or bring in from out of faction.

Best Runner Cards:

Actions:
Diesel: Card Advantage!
Sure Gamble: Much more action efficient than Easy Mark or Armitage Codebusting.
Special Order: Right now it's the only deck searching for the Runner, and the best way to get just the breaker you need at the right time.

Programs:
Best Sentrybreaker: Femme Fatale: Not only does she break Sentries, she lets you pick a 2nd ice to break cheaply. Only downside is that she is pretty expensive, and prohibitive against large sentries.
Best Wallbreaker: Battering Ram: Most money efficient during the endgame.
Best Codegate Breaker: Gordian Blade: Same as Battering Ram
Best Allpurpose Icebreaker: Crypsis: Having to spend time to get tokens seems like a pain, but in the long run its much cheaper than Wyrm.

Netshield: Very awesome against Jinteki, or anyone with Netdamage.
Sneakdoor Beta: Forces the Corp to defend Archives. Good for anyone, if you can find the memory.

Hardware & Resources
Any Console
Akatatsu Memchip: Currently the only non-console way to get extra memory (unless you're playing Djinn, which only works for the virus deck.)
Icecarver: Will save lots of money over the long run.
Wyldside: Well worth the time investment over the long run.

Best Corp Cards:

Operations:
Anonymous Tip: Card advantage.
Scorched Earth: Instant victory
Archived Memories: Recurse your best cards.
Neural EMP: Direct damage, no need for tags or tracing.

ICE:
Best Sentry: Archer. Forfeit an agenda for an extremely efficient killer.
Best Wall: Heimdall 1.0: Brain damage and 2 end the runs.
Best Codegate: Tollbooth: Very expensive to get past.

Assets:
Melange Mining Corp: For when you absolutely need money right now.
Project Junebug: Probably the best trap card, since it can kill the runner outright, and has a low buy-in for out of faction play.
Redherrings: Cheap for you, annoying for the runner.
Zaibatsu Loyalty: Make a run irrelevant for 1 bit.

Best Agendas (a little tricky, since all of the faction agendas are in-faction only.)
Accelerated Beta Test: You'll want to have your archives protected or know what's on top of your deck (Precognition, anyone?), but free ice is free ice.
Breaking News: A same turn agenda with no downside, or hold onto it for next turn for bonus tag goodness.
Priority Requisition: Valuable, and the free rez can be worth more than you paid into the agenda.

Willow said:

Over on the Board Game Geek forum Netshield is considered to not be stellar. Playing an upfront cost to be able to ignore the first point on Net damage each turn for one bit qualifies as kinda useful against Jinteki. (You would probably need an action to get either the card or the bit back) It doesn't stack with more copies, isn't very useful against other Corps, and takes up memory. Not really what I would qualify as a Best Card.

Willow said:

This prevents Exposure not Accessing. It stops Lemuria Codecracker and Infiltration. It does not stop runs. Good for trap based decks but not always useful.

That's good to know about Zaibatsu Loyalty- I'd been playing it quite wrong.

Zaibatsu Loyalty doesn't end a run. It only avoid a card to be exposed. Expose and access are two different things.

Nisei MKII is the best agenda in the game by far in my opinion. The ability to end a run at will is extremely powerful.

I would argue that the best ICE is not the expensive ones with fancy subroutines, but rather the cheap ones with the only subroutine that matters: End the Run. My list of the best ICE by type is: Wall of ICE (still costs 2 for Battering Ram to get through this little guy), Rototurret (Don't have a Sentry breaker? Well you don't have an anything breaker now…), and Enigma (Lose a time and end the run? Don't mind if I do.

Also, badash56 is right, Nisei MK II is easily the best Agenda in the game. I actually think Accelerated Beta Test is probably the worst because it trashes cards you wanted to see, and the only way to set the top of your deck costs 3 influence out of faction (Precognition).

In my opinion,

posted bounty is above, beyond, and miles ahead of any agenda as being the worst.

Accelerated beta test, precog deck - with archers and other gnarly ice is awesome. Now, I'm not convinced it is better than MkII, but I've had 2 free rezzes on archer… 20 bits to break that

I don't want to say which corp is "better" than another, because that all comes down to play style. I'll just say that HB in general "fits my play style" much more than Jinteki.

I'm also liking:

Corporate Troubleshooter - Such a nasty surprise. Can win you the game, if done on a respectable piece of ice. Also makes the runner very cautious about runs, which lets you sneak some underprotected agendas past him.

Stimhack - The good old Lucidrine Booster Drug (formely known as). This card has probably been responsible for winning me more Runner games than anything - although Medium is up there too.

Medium - Wow, what a virus. This makes any corp have to shake in their boots about defending R&D. Hoping they reprint butcher boy as well! In fact, I'm very impressed with all the virus cards, but this one is really a game winner.

Bank Job - Almost always worth its weight in gold… literally.

Account Syphon - Can turn the game completely in your control.

Precognition - So much better than basic card draw, as drawing more cards increases the chance of introducing more agendas to the game.

I'm Disliking:

Data Mine - Depends on your play style, but purely card advantage, it is not that great. Would be nice if it had a rez cost, and did 2 net damage.

Decoy - Sure, it may be a utility card against NBN/Weyland combos, but for pure efficiency, it is not that great. Rather see crash space, if anything.

The weyland identity card - so very underwhelming.

But, you know, FFG did a really good job with the core set, and even if I may not like some of these cards, they could certainly be made viable for some other people's tastes.

My favorite agenda is the NBN 3-cost agenda that allows you to advance something. It's neat to be able to chain advance things…once you get one of these in play, you can play and advance a second, then third copy all within a turn (each agenda takes its own turn). In other words, you don't need to use ICE to protect it, and you're essentially saving two clicks each time you use one of the advancement counters. The last copy can then advance Breaking News, which only requires two advancement tokens to win.

While I've never had the opportunity to completely advance 4 agendas in a row like this, I've chained multiple 3-cost agendas. The NBN strategy thus allows for flexibility…tag and flatline whenever possible, quickly rush through agendas when the opportunity presents itself.

As useful as the Jinteki agenda is, and it's super useful to wear through an opponent's credits (let them make an expensive run, then stop them before they access the card), Jinteki's playstyle tends to be very credit-intensive. I like the ability to push through agendas quickly and cheaply without an opponent having the chance to run on them multiple times. But then again, I personally prefer the NBN play style that gives me more control over Jinteki, which feels highly reactive and always on the defensive.

I think Stimhack is probably the best runner card in the game right now.

ironchefzod said:

Stimhack is good, but it is a little weak due to the fact that there are no handsize chips for the runner. Once they come out with some MRAM chips stimhack will get much better.

Outside of any Weyland card, Snare is one of the best cards in the game. You don't even need to play in your deck for it to be effective. Simply make sure you are leaving four credits available every turn and watch the runner completely rethink how they run. With the exception of Scorched Earth, no other card has this much power. Plus, a occasional flatline is also fun. A little smoke from the ears… Ha! Love playing the Corp.

No Aesop's Pawnshop? IMO that has to be one of the better financial options a runner has, and can only get better as more cards are released.

DeathByLiche said:

Even without handsize chips it's still ridiculously good. It has a run built into it so it refunds the click to play it and gives you 9 virtual credits. No other card has near that efficiency. The brain damage doesn't matter if you win that turn. I even use it mid-game when an opponent tries to rush an agenda through because I have no credits. I'll just stimhack in and trade a brain damage for an agenda.