This is, hands down, my absolute favorite bar in Las Vegas. I don't often hang out downtown, but when I do, I always head to Commonwealth. The decor is so awesome (and they decorate for Halloween!) and their Irish Jackass Mule (made with Whiskey & Lime Juice) cannot be beat. As for prices, it's pretty average ($12 mixed drink) by Vegas Standards.
What I love most about Commonwealth is that each time I've come here it's been a memorable experience and I've met some of the most interesting people from all over the world! Even heading in stag (not looking for anything in particular) men and women alike are just so willing to chat!
Oftentimes the live music is rockabilly inspired, which I love, but when they've got a DJ it's a great time to head up to the rooftop, get your groove on and view Fremont St from above.
Commonwealth is also home to "The Laundry Room"...but you'll have to do your own research to figure that one out!