I think candidlynuts is one of the most memorable and minimus and blondie. Really distinctive - to the point I now see those images when I think of those people...
The problem is some of the avatars are soooo teensy so we dont really notice what is in them - like the cute nurse and the man holding a pig - I didn;t know what they were - but then I might need my eyes testing so I won't rule that out.
The strongest are ones with a single close up image and they tend to stick in the mind.
JHRat is another one that I remember well! LOL