Down for me, too. However, it's a bit pricey for those on a budget. The Western Mountaineering Ultralite that I bought in 2006 for $315 is, last time I looked, edging close to $500. At some point, it's going to become cheaper to raise your own geese! If you have the money, though, a high quality down bag is worth the price. Properly cared for, it will last a lifetime, while synthetic bags tend to loose a significant amount of loft after 5-6 years. The cost per year of useful life is definitely less, assuming you have the $$$ up front!

Sleeping bags with lower quality down are, of course, heavier than the expensive ones, but not nearly as heavy or as bulky as your synthetic. Check out the Kelty Cosmic Down. Properly cared for, it will last far longer than your synthetic bag. It's often on sale, so check numerous vendors.

A quilt is another possibility. I am not a quilt person, but many experienced people here swear by quilts from Enlightened Equipment. I suspect they don't toss and turn as much as I do.

Don't forget that a sleeping pad is a very important part of your sleeping system. The ground is often colder than the air. Even more important, the part of the sleeping bag that's under you gets squashed flat while you're in it, so has far less insulation.

It would help to know where and at what times of year you backpack.