I realize that I am also an American tourist but I'm extremely lucky to have Matt there with me at every turn as I explore not just the world but specifically his home. So when I first arrived in London two summers ago and he handed me something called an Oyster Card, it never occurred to me that other tourists (American or not) wouldn't know about it.
|This is an Oyster Card|
If you buy an Oyster Card in London (at any tube station, some London travel info centers or oyster ticket shops) you can purchase a standard pay as you go card for a small deposit. Whenever you are running low on funds for traveling you can top it up at any tube station and be on your way.
You could also order a Visitors Card online for a certain set amount (with a card fee). The best part about buying a standard pay as you go card is that when you leave, you can turn it in and get your deposit back. For full (and probably clearer) details you can visit their website.
Oyster Cards all come with holders similar to this:
|They can have different designs though|
It's so difficult to learn the tube for the first time let alone try to figure out the (rather complicated) ticket system as well. I really hope that this helps make getting around to the amazing sites of London much easier.