There's a lot of recommendations for the Shure SM58 but there is something better for cheaper, and that's the AKG D5. There's a shoot-out comparison on Youtube, and judging by all the reviews I've been finding, it's universally agreed that the AKG is an SM58 killer.
After seeing lots of impressive examples of people on Youtube using it, I recently purchased a Behringer B-1 condenser microphone. It's not only a lot cheaper than a Shure SM58 but it's also a lot better. A high quality condenser microphone for the price of an AKG-D5 dynamic, but with a shockmount, windshield and very fancy case to go with it. I checked out all the forums and reviews I could find and it seems that the usual detractors of the Behringer B-1 are those that have never even tried it, just because it's a Behringer. From what I have read, it's a reverse-engineered version of the Studio Projects B-1, but for half the price. It's sensitive, it's sharp, it's great quality, and it is great value.
Another update 02.03.2012.
I eventually bought a Behringer B-1 and found I couldn't get my vocals sounding nice - they were very harsh and it often created irritating little metallic artefacts on the vocal track. I loaded the sound file into my Audio Editor (Magix Music Editor 3.0) and found it to have a lot of spikes; I suspect that is what's causing the harshness. Anyway, I became disillusioned with it and just bought an Audio Technica AT2035, and it's proved to be so much better, in another class. I now find that my vocals are far more in tune, and less takes are necessary. I've only used it for vocals and am very impressed. The Behringer will be going on Ebay.