Depends on what you plan to use it for. I can't say that I have ever really owned a crappy sleeping bag. Currently I have a 30 degree Kelty that I use for Hunting camp and tent camping. I have a 20 degree Slumberjack (Love this bag) that goes on my backpacking trips.

Your budget will also determine how good you think a bag is. Me..I can't see spending over $100 for a bag...but then I'm cheap. I have heard that the North Face Cat's Meow bag is pretty good and has gotten good reveiws. It's a little harder for me, being 6'1 and 220, I am tall and am pretty broad so standard mummy bags don't fit me.

If you are going to be using it for backcountry use, I would definitely suggest a name brand. My Slumberjack went down to single digits this year with a fleece liner.

I would also suggest getting in a bag before you order. You'd be surprised at some manufactuers really can't measure very good....well, then again I only had to test because of my size.

Shop around. REI and Campmor have good deals, you might also try Sportsman's Guide. They generally have nice quality for cheap...although they never tell you how much the bag weighs....so if you are wanting for Backpacking not a good site.