I did have a visa for Australia, because they require it. The UK website says people from some countries, including America, don't need a visa to stay for up to 6 months, as long as we don't work. I didn't have any trouble getting into France without a visa, and I should have been fine without a visa for the UK, because I was following their rules. Unfortunately, I was told after the fact that a visa would have given me a right to appeal before they put me on the plane out of there. I'll certainly apply for a UK visa before I try going there again. I still have the proof that the border control guy was wrong, and will use it if they try to turn me down.
If I were you, Chad, I would apply for a visa and see what happens. If you get the visa but they try to turn you away at the airport, the visa should give you a right to appeal. Then again, I don't know what country you're from, so you should check with UK immigration and make sure before trying again.