Dude, I backpacked all over Europe after college.....here are some places that I think you have to hit.
1. Amsterdam-obvious reasons but the art and history there is amazing.
2. Interlaken,Switzerland-This is the birth place of all extreme games. Its up in the alps, gorgeous town, lots to do, beautiful cheap hostiles-nice women:) But one of my favorite places to be.
3.Bacharach,germany-There is a huge castle there that was converted to a hotel/hostile.Cheap and you have a great view of the Rhine. I also met some gorgeous Norway women there.
4.Lugano,Switerland-This lake is huge,it borders Italy and Switzerland. You can go from one side to the next. Its funny seeing palm trees in Switz though...But by far a beautiful place.