Hee Haw Breaks is good to start you off so you can just have a mess about with loaaaaads of different stuff, absolutely packed.
Scratch Revolver 1 and 2 are both fucking awesome too, full of original samples and sounbites. if you want beats then pick up some Dirtstyle stuff, Dirtystyle Shampoo is sick, Stonesthrow are also sweet
I've found the best ones to be the skip proof ones - Done by the hardcore DJ's Sy & Unknown (They used to do the 'this is for the DJ' series).
They repeat the sample over and over for a few grooves so if the needle jumps a little (which i find a lot when scratching on battered 1210's with fucked needles in the pub function rooms I play in) you stay on the sample and dont have to pull it back / move forward on the vinyl) >>>> does that make sense?
I love them and personally wouldn't use others again.