Games: Third blade, Tiny wings, Street fighter 4, Infinity blade, Impossible game, Cut the rope, Angry birds,
Photography: Instagram, Photoshop Express, Spy kit, CameraArtFX, Fisheye Lens.
Social and browsing: Heywire (REAL free text cell messages), Skyfire (flash support browser), Skype, Justin.TV
Musical; If you play bass or guitar, I highly recommend you to get Guitar Pro, Tempo, iAmDrums, and Four Tracks.
Other: iDiscrete (the best app I've found so far to hide stuff you don't want other people to see if they get your iDevice for any reason)
And.... those are the apps I use more, hope you like 'em.