what's wrong with small avatars? I likes em small or non-existant. Don't know about you all, but when I logon to a forum and I see all kinds of self-indulgent 'look at me I have the biggest baddest weirest avatar evar!' crap, I immediately think the forum's gone to the crapper and has a decreased chance of offering me anything useful. 100x100 wouldn't be bad, I suppose, but I think the smaller size lends a bit of credence to tastefullness (avatar content withstanding) while still allowing some individual expression (if desired).
ok- I'll shutup now. brief rant over. avatar away.