i'll throw my .02 in here, yes getting wider than 28mm is really important, esp at wdw, i took some of the same pics from the same places for years, finally got the 10-22 and can't believe the changes in perspective, what's now in the shot etc. really opens up whole new areas of creativity
and i would explore other options besides the 28-135, it was a good lens back in the day, but it hasn't been upgraded since issue, the IS is the first gen, oldest IS canon has, how old, why i won grand prize in a photo contest with a pic taken with that lens, mounted on a d60, those familiar with canon history will know that's 3 models prior to the 40d
if you think you'll go full frame some day, go with the 17-40, it's a little wider than the 28 end, if you see staying crop for awhile, by all means try to finance the 10-22, i took mine on the med cruise back in may. it really shined in the narrow streets of europe, and allowed some real good almost pano stuff in plazas, much as you would get shooting wide in the open areas of the parks