I saw in the online newspaper ABC that Madrid Card has just released a special Madrid Card Navidad (Christmas) that only costs 20 Euros. The Madrid Card offers, amongst other things:

● Entry to over 40 museums (like the Prado, Thyssen and Reina Sofía)
● Unlimited travel (Bus, Metro & Suburban Trains)
● Guided Tour of Hapsburg Madrid and
● Discounts in bars, restaurants and shows

These cards can either be bought online or at hotels and tourist offices. Here are the prices as displayed on the Madrid Card site:

● The 1 day card: 28€.
● The 2 day card: 42€ – 4€ discount when you buy it on the website.
● The 3 day card: 55€. 5€ discount when you buy it on the website.

Though I’m not sure how ABC do their maths, it might be worth doing yours beforehand to see if it is worth the expense.
*Update* – El Mundo newspaper points out that the 20 Euro rate is for a 2-day pass.