Many have asked for some resources on lip syncing. Thanks to the community members of the main site, I can present to you a few to get started with.

Up first is a classic tutorial, DJ Nike's How to make lip sync easy.
A great resource, that provides some tips on how to break down the lip sync and recognise the different parts of the mouth and jaw that come together to form dialogue.
Mouth-a-mation
Next up, Spline Doctor and long term Pixar Animator, Andrew Gordon, provides some great advice within his mouth-a-mation post. The post creators pointers as opposed to a step-by-step tutorial, but certainly highlights areas that can help guide you.
Pandamation's Tricks #7

Keith Glass's offers a greatly detailed three part tutorial, that is well worth checking out!
This recently produced tutorial by Lester Banks, offers another great method of tackling sync. Using a method of recognizing and working with visemes, introduced in Jason Ospia's Stop Staring (definately worth checking out), Lester provides a detailed walkthrough. Well presented, informative and a great addition to the club of sync resources.
Please click the pic to view the tutorial.

Remember, these tutorials although offering different ways to tackle this challenging subject, there are many different methods available. You may even find your own. Always keep yourself open to new ways of thinking, and with plenty of practice you could create some well talked about bits of work.
Good luck and keep animating!