GPS can drain batteries quite quickly in my experience. Also, applets that are constantly active (for example if the reader constantly scrolls of fetches content). Note about rss - appLICATION or appLET ? Skype is also a hog, but to a lesser extent.
I just enable offline (a.k.a. flight) mode. That usually is enough for the usual suspects to refrain from causing trouble and in my case I loose less than 10% of battery through the night.