Sleeping Bag Guide
1. Size -- Some of the higher end bags come in short, regular and long sizes. The weight difference is very small, so if in doubt, get the larger bag.
2. Weight -- Be serious about what you are using the bag for. You really don't need a two and half pound bag if all you do is car camp (camp within walking distance of you're vehicle). Also if you are doing a lot of backpacking, get a good bag that fits your budget.