If roominess and weight matter more to you than the lightest pack weight, rectangular sleeping bags are a good choice, and they cost a lot less (in general) than mummy-shaped sleeping bags.
At Amazon.com, owners like the Coleman Andover 40-Degree Rectangular Sleeping Bag, which uses four pounds of polyester fiber insulation with a polyester cover. The sleeping bag is flannel-lined for coziness, is designed to keep the zipper from snagging and has an exterior pocket to keep a watch handy. It's 75 inches long, sized for people up to about 5'11" tall. The bag is washable in a big commercial front-loading washer, and carries a five-year warranty. For people as tall as 6'3", the similar Coleman 30-Degree Sleeping Bag - Bluespring (Tall) is 80 inches long. The main drawback is that owners note shoddy construction on several other Coleman sleeping bags priced about the same, which raises some doubts about quality.
The L.L.Bean Flannel-Lined Camp Bag comes in a kids size plus two adult lengths, Regular (*Est. $60) for heights up to 5'11", and Extra-Large for people up to 6'5". Owner-written reviews at LLBean.com confirm that these nylon-covered sleeping bags hold up well after repeated washings, and we found no complaints about workmanship or zipper snags. This sleeping bag comes in six colors and the stuff sack can even be monogrammed (*est. $6). Quite a few owners say this sleeping bag is also comfortable as a quilt, fully unzipped to lie flat.
For even warmer nights, owners like the L.L.Bean Cabin Fleece Sleeping Bag. Reviews say the polyester fleece feels very cozy against the skin. This bag is just a soft fleece bag with a zipper and without any outside cover, but you can also use it as a liner inside a regular sleeping bag. Experts say a liner like this extends the temperature range by another ten degrees or so. The Cabin Fleece sleeping bag is only 74 inches long, however.
For taller users, the Columbia Bugaboo II 55-Degree Rectangular Liner Sleeping Bag is 80 inches long. It has a cozy fleece lining plus an outside cover that's somewhat like a smooth high-quality sheet. Owners reviewing the previous version at Amazon.com say it's perfect as a sleeping bag liner, for tropical nights or whenever you want a very lightweight sleeping bag – as on a cycling or ultralight backpacking trip.