Originally Posted by cyccommute
Unfortunately, most mountain bikes now don't have the capability of mounting a rack, especially high end machines (I've paid my dues and don't ride cheap bikes anymore
) I also think that mountain bikes make the best commuting bicycles around so we have to deal with the lack of rack mounts either by using a seatpost rack
or pay premium bucks for an Old Man Mountain (which I don't like much either) or Delta now makes a
disc rack. I have one on my hardtail that has disc mounts and no rack mounts and it works well. It's a little light, I wouldn't use it for loaded touring, but it's a great rack for commuting. It would work well on other bikes that don't have rack mounts too.
Unfortunately this is mostly true, however it is still possible to mount a light duty full rack with P-clips to a hardtail MTB. My Ascent Horizon / Blackburn Expedition came with a pair but you would need 4 if your bike did not include the upper mounting bolts. I wouldn't use this method for a heavy touring load but it should be sufficient for commuting and its still better than a seatpost rack.
I've seen the Topeak racks and trunk bags in the LBS and it really is a slick system. Most trunk bags are not difficult to attach but the Topeak system is quicker and more secure. Its what I would buy if I was purchasing now.
Craig