Keep warm: Depending on how you heat your home/apartment, a really warm sleeping bag isn't a bad thing to have. If your method of heating went down in February during one of our cold snaps, it would be pretty nice to crawl into a -40* bag. Good sub-zero down bags aren't cheap but will last a LONG time if properly cared for.
Keep cool: I've used these (http://www.westmarine.com/webapp/wcs...6#.UijbEEIiKIU) for weeks on end in 90* heat/humidity when the power was out and they work really well (you need one per person and use it close to your head when sleeping). They are intended for people who live on sailboats but work very well anywhere you need them. The previous version had foam rubber blades so if you stuck your finger in them while you slept it was no big deal. I'm sure they've kept that in mind with this version. At 300 hours per set of batteries, it's good for a solid five weeks of 8hr nights.