Some might have already mentioned it, but the Nose-pinching RC is a great one. You just pinch your nose and try to breathe through it. If you can, you're dreaming.

You can also try to count your finger, try to fly (not through jumping off a window!) or even try to use telekinesis. It depends.

Remember the idea of RCing is not to really confirm you're in a dream, but actually ask yourself if you could be. You might be sure you're awake now, but when dreaming you'll be just as sure. RCing should get you into the mindset that anytime, anywhere you could be dreaming. After some practice with RCs you won't even need one to confirm you're in a dream, but rather to ask yourself if you're in a dream or not.

Finally, it seems LaBerge found out that oversleeping helps a lot with LDing. So, wake up a bit earlier than you would normally, stay awake for that period, and when you'd be waking up, you go back to sleep. I've had personal experience with this, but now it seems LaBerge made it scientifical. Anyway, try it