I have a dSLR (Canon Rebel) but in the couple years I've had it, I haven't taken the time to actually learn how to use it in manual mode. It's my goal for this summer. I'm looking at some online classes to take but found this SLR simulation that is awesome for practicing manual.
Paper Heart Camera wrote a nice tutorial about going manual and included this photography cheat sheet.
I also like the post here and here is a list of posts that help with learning manual mode and taking better pictures in general. There is so much out there to help go manual, I suppose the only excuse I have is that I'm lazy. And that's not much of an excuse.