You can get free versions of Angry Birds HD, Seasons HD, and Rio HD that have limited numbers of levels - but if you're not overly addicted, it should be enough to last you a while. They even update the free version of Seasons with new levels for new holidays.
Also, highly recommend the AppShopper app - you can make a wish list and it will tell you if any of them do go on sale! I've gotten a couple good deals this way. And you can view the app's price history just like on the website.