If I am an American and want to come to the UK for an extended visit, have plenty of money saved, and plan to be a "tourist," do I require a return ticket, or can I just buy a one-way ticket? I have a place to stay, with a friend, and plan to stay as long as my passport allows (up to 6 months or less). In that situation, what would you recommend?
Before last year we would say that you should expect a lot of scrutiny at the border if you arrive without a return ticket and say you want to stay for the maximum allowable time, but if you can prove your finances are such that you do not need to work while in the UK (or, preferably, ever again in your life) and you can support yourself, then you would probably be OK.
These days you'll just swipe through the ePassport gates and you're unlikely to speak to immigration at all, but there is a small chance that the gates will kick you out to see a human being. In that case, the above applies.