I personally
hated MX Tabs. Couldn't go there without getting a dozen popups with each click. Perhaps they cleaned up in the 3 years since I last gave them a chance, but those few trips were enough to turn me off from it for good.
I'm surprised nobody's mentioned the
Bass Tab Archive, which has been one of the most reliable resources I've found in the time I've been playing. It started as the bass wing of OLGA, but kind of took a life of its own from there.
When I can't find what I'm looking for on the BTA (e.g. Spinal Tap's "Big Bottom"), I go to
http://www.allguitartabs.com