Just wanted to let anyone who is headed to London between now and May 2006, that the 2 for 1 offers are still valid.
We used a 2 for 1 voucher to go to Kensington Palace in November 2005; our one-day travel card was accepted as our train ticket. However, we actually cheated since the Circle Line was not operating that day and we took the bus.
If you plan on doing any of the major tourist attarctions in London and will be travelling with someone, print out these vouchers and take them with you. If you are travelling alone, I am sure you can find a friend in line who will split the cost with you.