There are two Hilton credit cards, each one offers a 40K point bonus. You could apply for both and have 80K+ in points after meeting the spending threshold. It's not too hard to do, especially if you stagger your applications so that you don't get the second card until you have met the requirement for the first card.
The first card is the HHonors Amex. No annual fee. Spend $750 in the first 3 months that you have the card. Automatic HHonors Silver status when you get the card. What I like about this card is that they also offer 5 bonus rewards points on restaurants, gas and groceries. So even if I'm not using it for a hotel stay, I can still earn bonus points for everyday purchases.
The other is the Citi Hilton HHonors Visa. No annual fee. Must spend $1K in the first 4 months of having the card. Automatic Silver status when you get the card and upgrade to Gold if you have 4 paid stays in the first 90 days of having the card.
Depending on the hotel category, 80K could be worth up to 16 nights of free stays. However, my experience has been that the minimum number of points required for one night is closer to 20K, not 5K. There are 10 tiers of hotel categories with the most expensive ones costing as much as 95K in points for one night.
I just wanted to throw those out there so that you have an idea of what you can get through Hilton, since most posters have covered Marriott.