A favorite and pretty traveled a lot is the one that starts off at the powerstation in Boulder city and heads down all the way to the Colorado river. You can get free off-road maps at the Lake Mead Visitors Center that are all labeled.
On the other side of the water is a loop that leaves from temple bar that goes down to the lake and does a loop up the canyon. I've seen wild horses and plenty of petroglyphs.
Just did a trip from mesquite 2 weeks ago.... Here
Nelson is an area south off boulder city towards searchlight, there are lots of trails most leading to lake Mojave and old mines. This is out at Fire Mountain Cove. But other popular trails are Copper Cache and Powerline to Aztec Wash.
My favorite trail is Wheeler Pass from Cold Creek to Pahrump, Wild Horses everywhere
Let's revive this thread for us southern nevadans!! Burro wash is one that also ends at the colorado river. They are also a few trails outside of Henderson which are fun, not really technical but fun nonetheless.