The 24-105mm L works very well with a crop, its just not a "all in one" walk around focal length. The images on a crop body are fantastic.
A little bummed about the 24-105 not working well with the crop but I'm glad I asked before purchasing
I use my 15-85 on my 7D rather than my 24-105 L because of the focal length issue. Its nice to have just one lens when out walking around.
I use the 24-105L on a crop and it suits me just fine. Sure I don't get ultra wide angle with it but it's more than wide enough indoors. I love that I can use it as a general all day walk around. I've even shot decent night pictures with it (in Manual) with a good flash or two. I've also shot concerts (before I had my telephoto) and it's got great reach on a crop. Personally, after seeing what the 70-200 2.8 IS II can do in terms of sharpness, I've got an itch for the 24-70II 'cause it's supposed to be as good. The 24-105 is good but the 70-200 is in another league. I'd save up for the 24-70 f/2.8 II if I were to do it all over again.
In regards to the flash, I'm thinking of selling my 430 exII. I like the controls on the 600ex-rt better. Just my spin. I'd rather get another 2 or 3 600's. Plus they're stronger (noticeably) when compared to the 430 exII. Sure you might not be able to feel the difference at first without a point of reference but from my experience, the 430 is just ok.