These lenses are so cheap you should just go ahead and get both of them. Sell the kit after you buy the 17-40 and nothing is lost! The 28mm on your 28-135 is not very wide compared to the 18mm on the kit. Trust me, it you do any landscapes, you'll WANT the 18mm.
IMHO, if you are starting out from scratch, and u want to play around and take snapshots and get used to your rebel. The Kit lens is the way to go simply on the fact that it is a wide angle zoom. With the exception of low light, the kit lens will be so much more verstatile compared to the 50.
However if you are saving up for a 17-40L (which i use)... it might be a good idea to skip the kit lens....
One thing with the kit lens is it seems to have a lot of copy to copy quality variation. When I bought my old D-Reb the kit lens that I got was quite poor, a friend had a copy that she thought was great, and it certainly seemed to put out some very nice shots. So if you decide to get the kit lens make sre that you check it out a bit and are sure that it is a decent copy before your time to return it runs out.
That said the kit lens IS a mighty good value and it is nice to have at least a moderately wide lens.
