You only have a few choices. The 3 most popular are Liberty, Eclipse, and Theory. Development has basically stopped (or it's @ a very slow crawl) right now. If you want lots of ROM choices, you might want a different phone. Hopefully things will pick up once ICS is available on the Bionic.
while I enjoy my Bionic, if you are looking for a phone that has a future with developers you might want to return it and get something else. Pretty much everyone has jumped ship for the GNex, Razr, Razr Maxx, etc, etc.
ICS is eventually going to come to the Bionic, but when it actually gets here is anyone's guess. I can almost guarantee that we will be running a fully functional version from dhacker29 long before an official ICS release comes from Moto.
The biggest limitation for this phone is it's locked and encrypted bootloader. If Moto would provide a way to unlock it, I would be plenty of people would want to develop for it.
I have to agree with jayman, a lot of the developers who were all for the Bionic jumped ship to either the GNex or Razr. dhacker has thankfully returned to the world of Romming (new rom for the Razr), so one can hope that we will eventually get an update on his stellar roms for the Bionic. His ICS Alpha build for the Bionic seems to be doing well with a few things here and there to work out.
But, if you're within your 14 day return period, you may want to seriously look at the Nexus, Razr, or even the Rezound if modding your device is your ultimate goal. Personally, I'm happy with [K]IN3TX as is. Granted I was mostly looking to get Blur off my device and debloat the thing.