What's a good, cheap flash?

More specifically, I want something that will just plain work on my 40D. I rarely use flash, in fact THISis about the only thing I ever use it for, and you can see the problem. What's a cheap solution?

I see the shadow from your wild angle lens If you know how to use manual flash, a Sunpak 383 is about $90.

If I can learn how to use a manual camera, I can learn how to use a manual flash
Sounds like it's just what I need.

Well, that image is interesting enough that you need some better lighting so we can see more.

I think your best bet would be a 430EX. It fits the good part, you decide on cheap at about $240. It is the bottom of the usable Canon line. (isn't that sad? $240 is the bottom of the line?) Since it's a Canon EX flash it will be compatible with your 40D.

Your lens is another matter. At 10mm I can't tell you how the flash will look. I know the pull down panel is supposed to be good to 14mm. Since I can't go wider than 16mm I have no experience there.

Unless as stated above you can go to manual flash.