I usually use ARIN for IP lookup in the US. There are 2 others, one for Europe (RIPE) and one for Asia that I can't think of the name for at the moment. They not only give you the ISP, but the abuse contacts as well. I prefer to go to those as those are the ones that other sites use for the same info. I prefer to go right to the source.
It's a bit deceiving for mine. It comes up as Dartmouth, which is actually a part of Halifax. They shouldn't really be listed separately. I suppose it is better to be more specific though. Even though it's wrong in my case.