Right now I only have an EF 28mm f/2.8 IS, but I plan to get the now patented EF 50m f/1.8 IS when it is released and something in the 100mm range.
First of all I got the 28mm lens super cheap, about $500 brand new when it was retailing for 800.
Second, I have a crop body and 28mm is a fantastic focal length for a general purpose lens on crop. Not too wide, not to narrow. Its almost like when I look through 28mm it seems like I am seeing the same FOV that my eyes are seeing where I point it. I got the f/2.8 IS over the f/1.8 because the f/2.8 appears to have far superior quality and the IS is nice too for low light. The 28mm is smaller and lighter than the 35mm, though it is a bit slower. Still, I think 35mm is not quite wide enough on APS-C and if I got that I'd also want a 24. 28, though, sits nicely in between the two. According to A/B comparisons online, the 28mm IS is also slightly sharper than both the 24mm IS and 35mm IS.
50mm I would like for portraits, but it is all-too-obvious we will likely see a 50mm f/1.8 IS by the end of the year. So I am not going to spend money on something I will inevitably sell within 6 months. This is nice for its fast speed and focal length on APS-C.
100mm I will probably go for the f/2.8L IS macro lens. It again has IS which is nice and it is a better performer than the EF-S 60mm. Plus, the 100mm allows you to be about 4" further away from your subject which is generally a benefit for macro. Plus it will give me more seperation from 50mm than 60mm would.