I'm looking for some tricky/difficult integrals within the scope of calc I and II that I can play around with. Most of the integrals in my books (Stewart and Spivak) are fairly straight forward, and the only real practice I get is in "rigor". I can't really make up my own problems either, because I always come up with something unsolvable (without a CAS et al). What are some good integrals??