How much? You might need to save it up from multiple socks. You might have enough for anklets or another pair of socks if you do the toes, heels, and cuffs in a contrasting colour. Fingerless mitts or even gloves with fingers can look cute, and in similar diameter to feet the stripes will be similar. Some people make scarves out of sock wool but you probably don't have enough for that. I think there's a blog somewhere with 100 uses for sock yarn or something similar... a nice accent on jumper cuffs and neckline? Strand it with a solid colour to make it go further? A hat? It depends how much you have...
ETA: here you go
http://golden-apples.blogspot.com/se...=101+ideas+for