the link above will show you the current ROMs available... however you asked for a stable ROM.. Fresh 1.1 is running Android 1.5 (just like your phone is now).. the current 1.6, 2.0.1 and 2.1 ROMs out are development ROMS and even though they work well are not 100% stable and none of then have everything working in then (BT, MMS, and camera seem to be the biggest thing s not working)
right now, for stable, I suggest Fresh 1.1.. then add the Gumbo kernel and the phone will be fast as well as stable.