Sometimes you just don’t want internet people to see your ugly mug. That’s a bit hard on Facebook, but with Twitter you have a bit more control over your ‘image’.
I quickly scanned through my ‘following’ on Twitter and scraped it for non-photos. I noticed a few trends: Sketches, silhouettes, and pure vector (this style always makes me think of this cover art).
An illustrated avatar is a smart route to take, because it doubles as a logo for yourself, but just remember, at least one person who sees it will know what you look like in real life. My favourite of this small selection is Andre Souza’s because he constantly customises it.