ShyGypsy

I remember being addicted to this online puzzle years ago: http://shygypsy.com/farm/p.cgi. It's hard for me to explain, but essentially you're trying to create a word map, starting with one phrase / clue: "on the farm". You guess words that are related to that phrase, and uncover more and more of the word map. Words connect to each other, moving further from the original phrase / clue, things get complicated, interesting and frustrating all at once, and you just have to try it to see what I'm talking about...