The rivers used typically include the Colorado River just across the continental divide, and the Poudre River just west of Fort Collins. Some companies will meet you at the disembarking point, others will include transportation to and from Estes Park. Some trips include meals, others just the guided rafting trip. All trips are guided and all equipment is included.
Some trips are fairly calm, others are totally wild.
Whitewater trips are generally available from May into August, depending on the run-off.