The 50D's noise performance is significantly better than the 40D. If 800-3200 shooting is something lynn ever really wants to do, this easily outweighs the small performance difference of the 10-15MPix. The gap-less pixel technology (forget the exact wording) has done some incredible things with noise performance. The 50D also has a much brighter, and better resolution LCD (~912kpixels vs ~215kpixels).
Other brands have some models, such as the Pentax K20D, Olympus E30, or Sony A700, which also are fine cameras that would meet your needs. But my caveat with any of these would be that the SYSTEMS may not meet all of your future needs as a working Professional, and the commitment of these companies to the professional market may not match that of Nikon or Canon.
Well, they've all remained committed to their base for the past few decades, don't suspect any will leave them abandoned. When Minolta had to retire they handed over their system manufacturing process to the very best company to take care of it, the number 1 provider of digital sensors in the world: Sony (subsequently awarding their base with Zeiss glass autofocus capability). I don't think worrying about the future of any system is realistic for any professional, each system is too marketable and profitable for any technology manufacturers to just ditch in a field.