The Tour De Lander website has some excellent route descriptions and profiles of some classic local road rides. Click on "route samples" to view them, after you're on their website:
Tour De Lander Route Profiles

Fairfield Hill is a good area for hiking mountain biking. Above is a good loop on it that I ride every once in a while.

A classic Lander Road Ride.

Once the road to Shoshone Lake is open (usually late June) this is a fun loop to mountain bike on. It's a 33 mile lolly pop and it usually takes me about 4 hrs round trip- from Lander.

Just up the road from Lander about 50 miles, there's some great mountain biking too. This is a loop we did up in that country a couple of years ago. We started in the East Fork, went up over Spring Mountain and down into the Horse Creek drainage. We returned to the East Fork via the badlands behind Dubois.

A great little loop to ride up the East Fork.

If you have permission to ride on the Homestead Park Road, you can actually ride almost all the way to the top of Fairfield hill. If you're looking to rack up the vert... it's a good one! You need permission though. Don't poach!
The "Bus" an area of BLM land along the Squaw/ Baldwin road offers some excellent mountain biking too. Hope to have some route info posted about that area soon. It's probably the closest and earliest MTB riding. It also sounds like our club will be partnering with BLM folks to do some work on this area. It seems interest is high in creating and preserving recreational opportunities for people in this area.
Other classic MTB riding areas around Lander include: Beaver Creek X-Country Ski Area on South Pass, Sinks Canyon (Loop Road/ Snowmachine Trail) and single track all round NF campground, Government Draw- off the Lyon's Valley Road, and Johnny Behind the Rocks (more BLM about 15 miles out of Lander towards Jeffery City). There lots more too.
If anyone has any trip reports, route descriptions, maps or info about riding in any of these areas that you would like to share with folks... email me and I'll get it posted.
Happy Trails!