I couldn't be without Zite and Flipboard linked with the app Pocket to view articles and videos later. If you want apps to "show off" your iPad to friends and family members I would suggest soundhound and Garageband. The best part is all of those apps, besides Garageband, are free.
If you're a gamer, you can download my CSS tribute app, it's always fun x)
and SoundReaktor is a fun music app, there's so much to download.
My favorite free apps are google Chrome, Flipboard & some games. But it all depends if you're into gaming or not.