travel card in London

Sounds like you already know, but no Travelcard will take you out as far as Windsor. You'll need to buy a separate ticket for that.

It all depends- how long will you be there and how many people are traveling together?
If you will be there less than 4 days (doesn't sound like it from your brief description), and there are at least 2 of you, you might want to get single day PAPER travel cards from a NATIONAL RAIL STATION in order to take advantage of the 2-for-1 admission deals and discounts offered by the National Rail service. These cards are good on all buses, the Tube in the ed zones (usually zones 1 &2 are enough for tourists) and often get you a discount on that Thames cruise. You can also get 7 day PAPER travel cards from NATIONAL RAIL STATIONS with the same benefits. Again you the zones (if you want full 'availability' then get zones 1-6, but zones 1-2 are usually sufficient). You will need to bring or buy a passport sized (but not passport quality) head and shoulders photo for the free, but required ID card for the 7 day travel card. This is usually the most cost effective purchase if there are at least 2 adults who will be in London for at least 4 days and who want to use the 2-4-1 deals. You can research those deals here ( http://www.daysoutguide.co.uk/). And you might want to go ahead and print out any vouchers for the sites/restaurants, etc. you are interested in as some stations run out of the brochures regularly. If you are alone, or don't want to take advantage of the 2-4-1 deals, get an Oyster Card (looks like a credit card). You pay a deposit that is refunded if you turn in your card at then end of your stay. You can load some pay-as-you-go (PAYGO) cash on the card, or have a single or multi-day travel card loaded onto it, or both. The Oyster automatically calculates the least expensive cost for your day's use each day. Any left over PAYGO cash is also refunded when you turn in the card, and you can reload it as needed. These can be purchased at TUBE stations.