I recently picked up a Nemo sleeping bag with the vents and easy-zip system. It's amazing. Best sleeping bag I've ever owned. I've also owned an expensive Western Mountaineering and a Montbell Stretch (which I enjoyed). But the Nemo seems to be on a totally different level. The internal and external vents actually work and the pillow system is awesome. The bag also comes with their standard lifetime warranty, which is an added bonus. I know they're slightly heavier than some others, but it's totally worth the extra ounces.
I'm not affiliated with Nemo, but I thought I'd share just in case someone was looking for a great sleeping bag. Anyone else out there who's had a great expereince with Nemo? I did a ton of research on sleeping bags before taking the dive and it was well worth the time investment.