Best resources on data recovery from corrupted OS X HFS+ partitions
The best free solution I've found is TestDisk. I have no personal experience with it, but I've heard rave reviews.

You can also try Data Rescue 3, a paid solution. I've used an older version in the past with good results. Problem with this sort of solution is that they can only recognize certain formats of files. But there is an extensive list of files that it can recover.

Of course, the best tip I can give you for data recovery is keep regular backups -- especially for laptop computers!