I can only vouch for Tony Hawk's Project 8. I owned it maybe 4 years ago for a short time. I didn't really like it. I don't remember if it had much physics. The I've heard Tony Hawk's Underground 2 Remix is better in general, even though it's a little older. Come to think of it I kind of want to try out the latter sometime. The PSP is definitely aged now so it's kind of hard to expect a powerful physics engine, especially since both the aforementioned games are 6-7 years old now.