With the update of the d2etracker site, there is now a handy new page which can help you find the ideal monsters to use as an open group in your quest.
If you use the tracker it will even show a selection specifically for the encounter you are playing (based on traits and selected expansions, but you can use it even if you don't make use of the website.
You can find it here:
http://d2etracker.com/stats_monster_attributes.php
It allows you to filter monsters based on what their abilities do, as well as based on health, speed and even their attack/defense dice.
For example: A monster that can poison, has at least 7 health, and a black defense die .
I'm still looking for feedback though. Maybe there are more filters that people are interested it? Maybe there are some additions you'd like to see in the 'monsters that can' dropdown?
Let me know!