First, Titanium Backup Pro. It's like $6, but if/when you get into ROMs and whatnot that require data wipes, it's essential. Next BootStrapper, and create a nandroid backup. This is an exact image of your phone basically and a great restore point if SHTF. From here, I too recommend Liberty 3. It's my favorite of the 4 or so ROMs I've tried.