I've written before about the wonders of the low-cost express bus network along the East Coast's I-95 corridor. Since the federal DOT shut down a good number of the chinatown lines, the situation isn't quite as friendly as it was when I wrote that post, but one company has been making the best of it. MegaBus, a subsidiary of British transport firm Stagecoach Group, has an extensive network of curb-to-curb buses across the eastern half of the country. They started with a New York-centered network, and now have services throughout the Northeast, Mid-Atlantic, Southeast and Texas. Their buses are clean, modern, and have sort-of-reliable free wi-fi and on-board power outlets. Best of all, the service is cheap, with fares as low as $1 (usually one seat on each bus) and generally in the $20 range.
Of course, since we live on the wrong coast, MegaBus is unfamiliar to most of us Californians. The company did run a Las Vegas-Los Angeles-San Francisco service for a time back in 2007, but it was poorly-marketed and soon cancelled. (I say it was poorly marketed because, as an ardent observer of all things transit, I didn't hear about it until it was facing cancellation.)
That said, there is some great news out today. MegaBus is back-- and not only back in SoCal, but they're introducing new service to Riverside! Service is available on LA-Oakland-SF, LA-San Jose-SF, LA-Riverside-Vegas, and SF-Sacramento-Reno routes. (Note that you can't buy trips for short segments, eg. SF-Oakland, SF-San Jose, or LA-Riverside.) Service will start on December 12th, and the first week's service is all just $1. Beyond that, if you book quick, you'll probably still get the coveted $1 for any travel you have planned. The new buses will serve LA Union Station and the Riverside Downtown Metrolink.
I should also note that MegaBus runs an around-the-clock schedule, with departures from Riverside at 1:30 in the morning. It appears that there are four runs daily in each direction, with every run on the LA-LV route stopping in Riverside.
So, officially, there is a good way to get to Vegas without a car. You should book now!