Most people don't know this but if you have a Railcard your Oyster card will be capped at 34% less than normal. Just take your Railcard to a LU ticket office to get the discount applied to your oyster card permanently.http://www.tfl.gov.uk/tickets/faresandtickets/singlefares/6769.aspx
If you hold a National Rail Railcard, you can get an Oyster card and have the Railcard discount entitlement loaded on to it. You can then use Oyster to pay as you go at adult-rate, but your off-peak Oyster daily price cap will be 34% lower than the equivalent adult-rate cap.
Holders of the following National Rail Railcards can benefit from the discounted daily price capping:
* Disabled Persons
* HM Forces,
* Young Persons.
You will need to get an Oyster card and have your Railcard discount concession loaded on it. This can be done at
* Tube station ticket offices
* London Overground station ticket offices
* Some National Rail station ticket offices