To Psion - Really really bad luck with first book choice, that's almost as bad as grabbing the Souldrinker's Omnibus heh, Ultramarines or Space Boyscouts (always follow the manual!) are really as lackluster as you can get. I mean really, what do you expect from a chapter who's greatest achievements include (but are not limited to) NOT arriving at the Battle of Terra in time to do anything, Getting their first company entirely eaten by tyranids, and losing the Damoclese Crusade? The 2nd Ultra's book was ok, but only because of the Deathwatch Killteam in it and interaction with the Mortifactor's chapter which added some actual characterization.
If you want Epic Space Marines, try the Ragnar series (very Beowulf-esque) and easy reads, 4th or 5th book even has some of the best interaction between 2 non-standard space marine chapters (won't add in any spoilers and whatnot).
Gav Thorpe's Angels of Darkness is another good one, pointing out the dilema any good GM can use in the upcoming Deathwatch RPG. Again, no spoilers but it's far from space knights.
As much as I can't stand CS Goto, I did like his Deathwatch books, again, for the characters of the kill team, as well as the first Grey Knights book as it actually has a surprise ending.
Dan Abnett's Iron Snakes book was good, and different from the norm, though you can probably push this off as space knights heh.
The short story book Deathwing had some fine pieces in it too for space marines.
The Horus Heresy stuff is good too, and I'm told the books Iron Hands and the two Armaggedon books about Black Templars are entertaining.