Dear Lewy Boy
Actually it's not a weird topic at all because many people do indeed encounter problems with US Immigration on arrival, particularly if it's anything to do with flying.
But to answer your question. If you are coming to the States just to rent aircraft and not to engage in a full time training course then no specific visa is required. You may enter under the Visa Waiver Program (a green arrival card) or if you have the B1 or B2 visa then you can enter for business or pleasure - whichever the category is and I can't remember which is which! Unfortunately most immigration officers will take a second look at you if it's anything to do with flying - that's just a legacy from 91/11 and there's nothing we can do to change that. They may refer you to what's called 'secondary inspection' for a few more questions or just ask you about your plans at the main counter, it just depends on how neurotic the officer is. But certainly show them your pilot license and give them some precise information about where you are going to fly and where you are going to stay. That should be enough to satisfy them about your intentions.