I think it was the first game I bought for my iPod touch back when the app store launched: Deep Green Chess (affiliate link) is a great chess game and now supports native iPad and Retina display resolutions.

One advantage to buying it way back when I did - the price is now $7.99 and I'm almost positive I didn't pay that much for it when I bought it. Free updates to original purchasers, even back from 2008. From the blog post announcing the update:

Even if you bought it more than two years ago, you’ll be able to run it on any of your current iOS devices. And at no point in time have you had a reason to regret buying Deep Green at a higher price, because it has stayed the same since after the short introductory period. If anything, price will increase as more features are added over time.