I was in New York recently and we saw two shows - Xanadu and Monty Pythons Spamalot. Both were excellent - fantastic evenings entertainment. You can buy tickets on the day of the show at a 50% discount from the official ticket office which is next to (or almost sort of under ) The Marriot Marquis Hotel which is located on Times Square. Tickets are sold at 3pm and when we were there people started queuing around 2.15/2.30. There is a lot of good natured banter in the queue and when 3pm comes the line moves very quickly. Yes, you run the slight risk of not getting tickets for a particular show but there is so much choice this shouldn't be an issue. Recommend that you ask not to be in the first three rows - we were the first row for one of the shows and felt the effect was spolit a bit as we were craning our necks. We paid around sixty dollars for the tickets. I would recommend going to The View bar either before or after the show - it is on the 48th floor of the Marriot Marquis Hotel and has amazing views and cocktails. And it revolves...what more can you ask for?