Hey,
I checked out a few sample cd's when I first got into making hip hop music because I figured that a lot of producers were using them...I was very disappointed with the quality of the samples that most companies put out.
Basically, you fork out something close to $100 for a bunch of sounds or loops that either suck or are cheap ripoffs of things you hear on the radio. I can imagine radio producers/imagers love to use them as music beds because they sound so 'now' and a lot are ready-made, but it wasn't worth it to me as I had some gear to make my own sounds with.
This was a few years ago, since then the internet has spawned all sorts of piracy and the prices have dropped considerably, and now sample companies are allowing you to download individual sample from their sites for a small fee.
I'm sure that most people here will agree that the best thing to do is to find your own samples. I like to take it a step further and warp them in a wave editor before dropping them into a track so that it is no longer recognizable and therefore becomes 'my' sample (and hopefully escapes the ears of publishing companies). That, or sample single hits from different sources for something like a drumkit...
Take care,
Nick