The X series of Christian Rock samplers is a great way to discover which bands you like and which ones you don't. These are full-length songs, just like the ones that you'd hear on the radio if the Contemporary Christian radio stations ever played this kind of music. They put one out every year and we buy it every year!
I bought this CD for my daughter for Christmas and it turns out the whole family (from age 10 to 42) loves it. I wouldn't say that all the songs are the hardest I have heard but they are definitly very very good.