I've merged in the post from the Android Hacks and Mods forum as your request is a device-specific one. The Apollo forum may be a bit slow, but you're far more likely to get input from fellow Apollo owners with a thread here.
To address your query, what are you looking for in a ROM, or what do you intend to use the device for?
As for where to find the ROMs, there are quite a few to choose from at
Galaxy 3 Android Development - xda-developers. The options may be a bit overwhelming, so if you can let me know what aspects are most important to you (speed, stability, customization, appearance, features, etc) I would be happy to help you make a choice and get up and running.