iPad can be a useful tool for GM. One of my favorite programs there is Soundboard.
Soundboard is basically a DJ tool for mixing sound sources. This can be good for evoking a bit of atmosphere to your game. Create a playlist in iTunes for appropriate music depending on the stories or encounters you have. In Soundboard create one or more soundboards for the music. Import the playlist as a whole to individual soundboard – you can have 32 songs per soundboard visible. Name the soundboard so you can easily find it.
Purchase or create some sound effects for example. There are quite a few commercial ones available from iTunes or Paizo website. Create new soundboards for the effects for example – drumming, ghostly sounds, combat etc.
During the game select from soundboard good background music for your particular situation, for example something from Lord of The Rings, Ennio Morricone, Epic Score or Midnight Syndicate. When you need sound effects just flip to the soundboard that contains the proper effects and click on each one you like to play for example growling and combat sounds. The advantages of Soundboard are that you do not need to search and click on iTunes playlists and that you can play effects, even multiple effects on top of each other and background music.
If you need more volume than iPad speakers supply, you can connect the iPad either to a stereo system wireless or to external speakers via bluetooth. Usually the iPad speakers are enough.
Campaign Mastery has a good article on creating the mood.