Adventure Passports publishes two great books that allow you to log your ascents of the mountains of Colorado.
The Passport to the 14ers features a checklist section listing all of the Colorado Peaks at or above 14,000 feet, and then the diary section contains a single page for each summit.
Each diary page provides space to record the date, your start, summit and finish times, difficulty, weather, etc.
The Passport is a convenient size for pocket or pack, weighing just 3.5 ounces. The cover is rugged, and should take a lot of abuse.
Adventure Passports has recently released Passport to the 13ers of Colorado, a companion log for the peaks between 13,000 and 13,999 feet. It is identical in form to the 14ers Passport, but the cover is maroon rather than green.
You can buy either Passport for just $8.95 at their website.