Earth Rotation Speed Variances?

So I heard that the Earth's rotational speed actually fluctuates quite a bit (relatively speaking), with the Earth spinning faster in September and slower in March. Some googling also shows that the Moon (and thus tides) has a significant effect on rotational speed.

I guess what I'm asking is what all the main factors for the variances are. Is it just the Moon, or are there other factors, such as perhaps the tilt and wobble of the Earth as it orbits the Sun? Also, how much are the actual variances in rotation time for the different factors?

Sorry to resort to bothering you guys, but my google skills really aren't doing me much good on this one and I figured you might appreciate seeing something besides the usual trolls, idiots, and homework threads.

A fairly strong earthquake is also enough to measurably alter the rotational speed.  After all, such a quake can shift trillions of tons of mass by up to 30 feet in a few seconds.

Jeepers

>>2
If by "measurably" you mean "not". An earthquake large enough to have that kind of effect would be enough to sink a continent.

Ass