Possible alternatives to 17-40mm f/4L?

So I've entered the world of DSLRs and just a bit over a month ago with the purchases listed in my signature without knowing much at all about photography (other than the fact that I needed to get outside the realm of point&shoot cameras). Within that time period, I've learned a great deal with my 30D and could not possibly have learned much without the company of my 50mm f/1.4 (what a great lens).

With that learning experience comes some realizations. Just this past weekend, I was at an auto show locally. I realized that my 50mm was way too long and had to stand at least 10-15 feet away from vehicles to get a full body shot of any vehicle. Obviously, since there were a lot of people there, it was difficult for me to get a clean shot of a car without having people walk in front (not that I blame them). After shooting a few cars with the 50mm, I realized that I had to revert to the kit lens. This is when I realized that I needed a better lens for wide-angle. I got some decent shots with the kit but wasn't too satisfied with the overall result. I know some of you have warned me about getting a kit lens initially but it was only a ~$40 difference between the kit and body-only and I saw them going on ebay for more than $40 on average.

Now, I want a replacement for my 18-55mm kit lens. I've been looking at the 17-40mm f/4L and read that while it seems to be the most popular L lens (since it's relatively inexpensive compared to other Ls), there may be other alternatives out there that might be a better investment.

I've searched the forum and find that current 17-40mm owners give great reviews on it but those who once had the same question I am asking now and went with another lens say something like "I'm sure it's a decent lens but I went with XXXX cause of XXXX."

I like the price range of the 17-40mm. At first, I was afraid to spend $300ish for my 50mm but after using it for over a month, I have learned that the most important thing in photography is the lenses you use so decided to make another investment to replace my 18-55mm while the rebates are going on.

My plan is to invest in a full frame DSLR sometime in the distant future so I would prefer a lens I can use with a 1.6x cropped and full-frame camera. If you could provide me with an alternatives to the 17-40mm with similar focal length ranges so I can do some research, I'd greatly appreciate it!

Thanks in advance!

Full-frame compatible there are pretty much the Canon 17-40, the twice as expensive 16-35, and the non-L 20-35, the Sigma 15-30, 17-35 and 20-40, Tamron 17-35 and Tokina 19-35 (avoiding super-wide lenses). The 17-40's got a rebate available now. Of the non-L options, it really depends on how long you want the long end to be. My widest is my Sigma 15-30 which is a very nice, if big and bulky, lens. But that would leave you a pretty big gap before your 50 could take over; you'd need to continue to carry the kit lens too. But all things considered, the 17-40's got the best range to serve as an 18-55 replacement and 50 complement. It's also a tad faster at the long end than the others, although at the long end your 50 would be the lens of choice. If you're ready to get something compatible only with the APS-C of your 30D, there are several fast (f/2.8) zooms that are close enough to not matter to the kit lens' coverage. Canon, Sigma and Tamron all make 17/18-50/55 constant f/2.8 lenses for the smaller sensor size, and they're all withi your price range.