I just had my radiator re-tanked. After replacing the rad, topping up the fluids and letting car idle for a while I noticed that the fan didn't turn on (there's only one, no A/C). I took the car to work this morning (good 45 min highway drive) and still no fan. The light on dash is not coming on (it does work) so I don't think it's overheated; yet. Where do I start tracking down this problem?

 

I don't think the fan comes on at over 30mph. Your sure its not comming on when its supposed to right (I think its 220-230, but i'm not sure)?

After that I would turn on the AC, and see if that kicks the fan on. If it doesn't I would check all the connections, if it still doesn't turn on you can try grounding the fan switch wire but I wouldn't bother, then the motor is probably shot. If it does turn on try grounding the fan switch wire, if it turns on the fan switch is bad, if it doesn't check the relay.
Oh, and I would check the fuse too

And do a search, tons and tons on fans.