If you are wishing to shoot sphericals for display on the Web then choose a fisheye - you will need far fewer shots and the resolution of the stitched pano will be quite sufficient to produce a FlashVR of good quality capable of fullscreen display on the Web. The Tokina 10-17mm zoom FE is a popular choice for Canon 1.6x crop bodies.
Spericals isn't my big interest (though if I try some, who knows, maybe I'd become interested). What I was considering the FE for is so the density of pixels was consistent across the range of projection, rather than going between more and less dense as the point in the pano moves from edges to center to edges of where the original images came in.
If you want to shoot partial panos with a pano FOV of less than 360x180 then consider a rectilinear lens. If you want a lens of shorter focal length that you kit lens then the Sigma 10-20mm WA is considered to offer very good value. Your kit lens should do fine for higher res. partial panos. In fact you can shoot sphericals with your kits lens (or any lens) - it just takes many more shots than using a FE.
My interest is in full 360 horizontally (viewable as infinitely rotating horizontally) but not all the way to 180 vertically. The kit lens is 18-55mm. 18mm is not quite wide enough in some cases, so I would look for something a bit wider. 18mm in 1.6x cropped sensor is about a 28.8mm in 36x24mm full frame. Something around 20mm in full frame, which would be 12.5mm in 1.6x crop, would be about right for rectilinear for what I want.
This kit lens is not that sharp, and has some chroma aberration in it. So I'd much prefer a fixed focal length. But there's nothing in WA fixed focal length specifically for cropped sensor. A lens with that focal length for full format would be overkill for a croppy like the 450D. I'm kinda waiting to see if maybe I'll move up to a 5DMK2 or something (plus re-invest in CF cards I can't use in other cameras).
Else I'll need to do multi-row panos using a less that very wide lens.