No-nonsense muscle building for skinny guys and gals!
Vince DelMonte's #1 Rated Muscle Program

The truth about muscle building for hardgainers.
NY Times #1 Selling Workout Regiment

As you can see, each of the programs are reputable in their own right. I ended up getting both, since there is a money back guarentee. I do recommend getting one, though, then trying the second if you are not getting the results after 3 weeks.