Due to the incredible amount of snow we've received so far in the high country this year, don't expect to get too far with the Rover on many trails until late July/early August, especially in the San Juans. We are experiencing the highest snowpack totals since '96, and it's still snowing.
Mud season will be a long one this year! Bring gaitors and full-grain leather boots that are waterproof or treated with repellant for hiking. Mesh hikers or split-grain leather boots will soak through quickly. Be prepared for afternoon rains everyday in the summer. Be sure you descend any mountain by noon, as you do not want to be exposed above treeline when the lightening starts. A waterproof breathable shell is essential, as well as wicking shirts and synthetic hiking pants and/or shorts and wicking socks. Cotton could prove dangerous at elevation; many people get exposed to hypothermia in the high country every season. It still amazes me everytime I see hikers in jeans and t-shirts carrying a plastic water bottle and nothing else, with kids in tow, above treeline in the middle of summer! Don't be one of those people.
In terms of camping near Boulder, it is pretty limited for a reason. Indian Peaks Wilderness is the closest that offers designated camping and an excellent trail system, but if you are packing it in, you will be required to get a backcountry camping permit. They are free, and you can pick one up at the Ace Hardware in Nederland. Also, Rocky Mountain National Park offers exceptional backpacking, but again, you will need a permit. Also check to be sure if there is a fireban in place in the areas you will be camping.
Drink water. Lots of it. More than you think you will need. A gallon a day is ideal when hiking at elevation. Perhaps look into a water filter and a camelback? Also, always tell a friend or someone you know where you are going, and when to expect you back. It can be 85 degrees in town, yet snowing and miserabe in the middle of July. Be prepared for anything.
I recommend a fly-rod and fishing permit for maximum hiking pleasure.
Chasm Lake is a must-see in RMNP, and it is an ideal weekend camping trip. Summit Long's Peak if you are up for it. You will not regret it. Reserve at spot at the boulderfield and prepare to be in awe. For more solitude, try the northern end of the park, in the Never Summers. Many of the lakes up there contain native cutthroat for catch-and-release. Moose sightings are common up there, and there are less crowds than you will get on the I-70 corridor on the weekends. As someone else suggested, the Sand Dunes are certainly worth a trip as well. Backpacker's got a great article on the dunes in this month's issue.
Rovering and camping. Two of my favorite things!
Oh yeah, bring a camera.