Canon EF 20/2.8
My first set of true SLRs was comprised of Minolta MD equipment: an SRT-201 and an XG-9. With those I had a decent but not outstanding 28/2.8 lens from a third party manufacturer. The perspective was good and allowed some near-far types of shots with a little effort. Image quality was just so-so. Looking for an excuse to spend the money that was burning a hole in my pocket I 'upgraded' (whatever that means) to a Canon EOS system.
For the EOS system there are several choices for wide angle lenses: the 28/2.8 USM (~$225), the 28/1.8 USM (~$450), the 24/2.8 with EFD drive (~$350), the 24/1.4L USM (~$1400), the 20/2.8 USM (~$500), and the 14/2.8L USM (~$2300 - ouch!). I wanted a rectilinear lens as I'm not too keen on fish-eye distortion. In addition, I wanted something wider than 28mm which always seemed a bit too confining since a lot of point and shoot cameras have lenses as wide as 28mm. The 28mm length just seems less and less unique. What's more, I wanted something a bit shocking in perspective, not to my wallet (leaving the 24/1.4L and 14/2.8L completely out in the cold). I may be an engineer that has done alright in the Internet Gold Rush but I don't have oodles of cash like Philip Greenspun. I also wanted a USM focusing mechanism. If you're going to buy into the EOS system don't waste your money on non-USM lenses. I've only had a little experience with non-USM lenses but I wasn't impressed with what I saw. With all of those parameters my options narrowed down to the 20/2.8 very quickly.
The 20/2.8 isn't a small lens. But it's not huge either like the 28-70/2.8L. It takes a somewhat pricey 72mm filter and weighs 14.2oz. (405g) according to B&H Photo. Due to it's size, be prepared to keep your on-camera flash turned off or you'll end up with a nice, dark semi-circle at the bottom of the frame. The f/2.8 maximum aperture is fine enough for me. The idea of having an aperture larger than 2.8 - 2.0 on such a wide lens seems almost useless unless you're taking a lot of shots of extremely dark interiors. If that's the case you might be better off with the 50/1.0L lens. With a 20mm lens it's pretty easy to hand-hold in available light if you stick to the limit of 1/focal length for your shutter speed.
I find the 20mm perspective rather pleasing and it yielded some interesting shots on my trip to Ireland. The images from this lens are sharp. Certainly sharper than the third party lens for my Minolta equipment. With the USM drive it's also very pleasant using the auto-focus. The design is retro-focus; the internal optics move within the barrel keeping the lens from extending or retracting. The filter threads are also non-rotating, coming in handy for grad ND filters (so I hear). I haven't performed any optical tests on this lens and don't intend to. I'm not somebody that really gets all that excited about super critically sharp photos - I'd rather just shoot and worry about composition. Is this lens as sharp as the 24/1.4L @ f/2.8? Probably not, but I've never used the 24/1.4L so I guess it's an irrelevant point for me. I also don't think the 24mm perspective is different enough from 28mm for me to have bothered with it anyway. What this lens does well is allow me to take interesting near-far shots and do it without hesitation that the optics will be distracting in the final frame.
As you can tell by now, I would recommend this lens over the other Canon wide-angles if what you are looking for is wider than 'normal' perspective with strong optics and a minimum of nuisance in hauling it around. It's also nice that it does all that without breaking the bank too badly (well, relative to the 24/1.4L, anyway).