My 17-55 lived on both my 40d and 7d. It was THE lens for those cameras. Sharp and fast with IS... as others have mentioned... it worked well on those two bodies, and had a very useable focal range.
Now that I have my 5d3, my 7d and 17-55 rarely get used. My 24-105 is on most or the time as a general walk around. If not I have my 70-200 or 85 1.8 for portraits. The 24-105 is a very useable and versatile focal range , decently sharp, and with the 5d3's high ISO capabilities, its very useable in low light, though 24-70 2.8 would be better...
Think really hard of why you're upgrading... I miss ultra wide as I don't have a lens that covers that yet on my 5d3. I luckily was able to keep my 7d and all my lenses as a backup, so I can still use my 10-22 and 7d when I need it, until I can pick up a 16-35 or 17-40.
5D MKIII|7D w/ Grip|EF-S 10-22MM f/3.5-4.5|EF-S 17-55MM f/2.8 IS|EF 24-105MM f/4L IS|EF 50MM f/1.4|EF 70-200MM f/2.8L IS|85mm f/1.8|35mm f/2 IS|70-300MM f/4-5.6 IS|580EX|Manfrotto 055PROB|2x PCB Einstein 640