I heart Hash House A-Go-Go.
I went twice with my friends in my most recent trip to Vegas. As many reviews mention, each time there was a decent wait - but the food was worth it. Everything on the menu looks delicious, but don't be fooled into thinking you can get two breakfasts if you can't make up your mind. Even if you're a big guy like me, you'll have a hard time finishing the one thing you order. So decide if you want delicious flapjacks, delicious eggs, delicious chicken and waffles, or a delicious skillet. But no mixing and matching or you might die.
As some have mentioned, the location off the strip is a little better than the one in the Imperial Palace. It's got better themed decor and a shorter wait. As far as I could tell, though, the food is the same at both locations.