The 100mm "Macro". Better image quality than some L glass, at a very affordable price.
I have this lens and it's one of the few I rarely use. The image quality is very good, but the bokeh it produces isn't suited for my taste. It's got a flat feeling to it and it feels very suited to it's actual application which is for macro work. It is a sharp lens and for the money it does a good job. I don't think the auto focus is particularity speedy though, but then again, most macro users probably don't even use the AF. The problem I would find with it for a normal usage lens is that at 100mm on a crop-body camera, it's in a strange rang of being a decent zoom, but not at all good for any kind of walk-around purpose.
I would probably even be willing to sell mine if macro photography was an interest. I probably have no more than 100-200 pictures taken with it and I still have all the boxes, etc. It's no longer in warranty though, since I got it back in 2006-ish. I got this lens basically for free after all the rebates that canon offered at the time when I bought it.
None the less, I support the idea that better glass will make for some more remarkable pictures. I've been the most happiest with the color, sharpness, and clarity of my prime lenses, but at the expense of some versatility. Investing in a decent supplementary lighting equipment will also go a lot longer than investing in the latest and greatest camera body.