I play two accounts, on one computer without the EQWindows program. On account 1 I have a 65 shaman, 50 bard, 37 mage, 31 monk, 30 cleric, and various lower toons. On account 2 I have a 55 Paladin, 23 enc, and various lower toons.
Often times I wish my cleric/mage were on seperate accounts, but I'm not going to pay to make that happen. Most of the time when I two box it's my shm/pal, with my best friend playing her cleric. I enjoy grouping still, and when someone asks for a group when I'm two boxing, I will invite them if I have over an hour to play.
I am working on getting my enc up to my cleric's level, and when I do that I will most often be 2 boxing them, with my (previously mentioned) friend's bard and ranger (she 2 boxes too).