I am so frusterated shopping for socks for my son. He is 5 and close to a size 1. I need a colored, foldover style sock for school. The quality of the gymboree ones is very good but they aren't strechy enough for him to put on himself and actually they are kind of a hassle for me too. The babygap ones are easier to put on (more elastic) but wear out before he has outgrown the size. The old navy weren't very good quality.
For the past few years, my son has worn this brand almost exclusively:
(Although not that style.) Might be worth a try.
Clearly we need to open a sock company!
Stride rite socks are pretty good - I was browsing through to see if I found any boys turn cuff ones, and didn't find any yet otherwise I'd link, but there were some boys dress sock style (doesn't fold down, however) that might work out (my kids never like folding the socks down, so something like that would be fine for them). They're a bit thinner and strechier than the gymboree socks and more like the gap fold over ones that we've gotten before.
Land's end has the same boy's dress sock style as the stride rite ones I saw too.
Sometimes department stores I never shop/look at have surprisingly good options for stuff like this. So you might want to check out places like that, if you don't already.