Moxie, of my beloved Ask Moxie, on managing the sock insanity:
Buy all the socks in one size in the same color, and then switch to a different color for the next few sizes. For example, buy 0-6 months in white, then 6-12 months in grey, then 12-18 months in navy, 18-24 months in red, etc. That way you can tell by looking which size a sock is, and you'll always have matching pairs.
To go along with the sock tip, here's a great Ask Moxie post on toddler shoes.