When I go into the Freakin' Frog, I know I'll have a good time. They have a huge selection of beers (about 500, methinks) and they often have live LOCAL bands playing as well (support your local musicians!!) in their newly expanded stage area. The bartenders are great and will remember your name and your favorite beer. The food is slightly better than your typical bar food, my personal favorite being the teriyaki burger.
Across from UNLV the bar is generally populated by lots of students, but mostly the Indie kids that might remind you of folks you would have seen in old Cafe Roma. Sometimes they watch movies or play chess while drinking a beer.
It's a generally open-minded place where people are genuinely nice to each other and enjoy meeting new people.