I have boated the Colorado River from Lake Powell to Martinez Lake and there are some really great place to boat on the Colorado River. Here's some of the area's I really enjoyed.

Powell is awesome just for the sheer beauty the Lake has to offer. From Petroglyphs to Indian Ruins and Natural Bridges to Rock Formations. We traveled from Wahweap Marina to Bullfrog Marina (a little less than 100 miles). We stopped at the Rainbow Bridge. I don't know if you can still do it or not but there was a set of docs to tie up to and hike up to the Bridge. The coves are also ridiculous. Some of the coves go back deeper than a mile.

I have spent quite a bit of time at Lake Mohave. Some of the cool places to go is Gasoline Alley there is a littler beach once you make it all the way back (you can jump off the rocks or just hang out) and Telephone Cove Nevada side (you have to get there by water or a dirt road but it's cool place to camp or just kick back and enjoy the beach). There's some nice coves by the dam but my favorite is to take a nice cruise to Cottonwood Cove to have lunch. You have to watch out for the wind in the big basin though. I have been out there when it is like an ocean and it's not fun.

I will post some more later...