Should we get an oyster for our 3 day stay in London. Also, it would be great to catch a play, any way to get good deals?
Re: theatre tickets, I always use the TKTS booth in Leicester Square (the heart center of the West End theatre district) for same-day tickets, available at greatly reduced prices. Not everything is on offer and it can change daily, so go early (as soon as it opens) and be prepared with a few options you'd be happy with if your first choice doesn't pan out. I never buy from any other 'discount' outlet, and you'll probably see several. http://www.tkts.co.uk/ If you're uncomfortable with waiting and getting same-day tickets, I've had good luck with ordering advance tickets from: http://www.lastminute.com/site/entertainment/theatre/
Maria, as you will be in London for only 3 days your alternatives are: 1. Get Oyster cards and add some pay-as-you-go credit to them at any ticket machine or ticket counter 2. Buy one day paper Travelcards each morning The maximum you can spend on Oyster is automatically capped at slightly less than the cost of a one day Travelcard, so if you only plan to do a few journeys then Oyster will save you money and if you plan to use it a lot then it will still save you a small amount. Oyster vs. Travelcard cost comparisons here: http://www.tfl.gov.uk/tickets/14416.aspx Note that most tourists will never venture outside of Zone 1, or maybe Zone 2 (for example, Greenwich)
The tkts booth is the small free-standing building in one corner of the square, not in a shop front. There are a number of shop front places in the area that try to impersonate it.
If you have put more money on your Oyster card, than you actually use, you can turn it in at any Tube station for a refund. After your last trip, just go to a counter and get your refund. It is very simple. If you plan on returning to London in the future, you can use your card at that time also. Oyster cards don't expire.