wireless tether (free in market)
im assuming you have rom manager and koush bootstrap recovery already if you're running flyx
titanium backup to save all your apps and data (free, but paid is neccessary)
or mybackuppro (4.99 i think)
adfree removes ads from teh browser and apps (free)
root explorer (4 bucks i think) but essential to moving around system files and installing a lot of stuff
terminal emulator (free) lets you do adb stuff on your phone
cache cleaner (free) does what it says
autokiller (free) basically enhances androids internal memory management
setcpu (1.99) lets you set processor profiles for better battery life
really for roms right now its flyx or tranquility...several others are working on a few currently, but the release of the new 2.2 last night may change their plans, im not sure