So many neat trips (that I want to do once I buy an Alpacka this summer); here are a few of my ideas:
-Muddy Creek to Dirty Devil. You could start at I-70, and do a mix of floating and hiking all the way down to Lake Powell. The first part would probably lend itself to more boating than hiking. The Dirty Devil part would lend itself to hiking loops away from and back to the river. Only issue is that it would be a better spring trip, with more water and fewer sandbars.
-Running the Escalante is high on my list, but again this is most likely a spring trip. You could hike the best sections of Allen's overland route (see Canyoneering 3) and float the bits along the river, thus avoiding the wading and bushwacking. Hike out Coyote and hitch back to town.
-Check out Roman Dial's "Candylands" loop in the Alpacka Forums. It's a nifty figure 8 of hiking the Needles and Maze districts and floating flat sections of the Green and Colorado rivers.
-Floating Labyrinth and/or Stillwater on the Green would be fun. You could throw in some side hikes, and find routes (Kelsey's books have some) to hike out to a car spot or shuttle on Island in the Sky.
-You could probably do something on the upper San Juan, but I'm unfamiliar with that river.
-The big daddy would be to do some sort of traverse or loop in the Grand Canyon. You'd have to walk around rapids, and I'm not sure how much downriver travel (if any) is legal without a boating permit.
For instance, I'd love to hike the Royal Arch route down to the river, float to Tapeats Creek, find a route out Saddle Canyon, then hike down the North Bass, cross the river, and hike back out the South Bass.