Canon 15mm FE is an awesome lens, the Sigma EX fisheyes are good as well, much better than they used to be.
Depends what you intend to do in the future, if your maybe considering getting a full frame camera like the 5d then i'd go for the Canon or Sigma 15mm, the Sigma 10mm is a APS-C lens. For the same reason i'd probably go with the 17-40mm over any of the EF-S lenses.
Macro wise, the Sigma 105mm EX is a great choice unless you want 'quick' AF then get the Canon 100mm USM. But optically they are pretty identical, even with a little edge on the Sigma.
Check
www.photozone.de for good reviews (all in english)