There is also a free app called presentation. I haven't used it yet, but just downloaded it. You can also buy a cable that has two ports, one to connect to the projector and one for your power cord so you won't run out of battery.
If at all possible, connect your device to a modern TV screen or PC monitor. All you need is a standard HDMI cable unless you're using an iPad or iPhone (All things Apple are "special" so you have to pay extra for their accessories). The European Commission are considering passing a law to prevent this kind of exploitation.
The resolution of almost all LCD projectors is shamefully low and gives fuzzy, difficult to read text on screen and very poor quality image and video reproduction. Try it out with your laptop before buying any hardware. Additionally, you have to block windows and darken the room in order to view projections whereas TV/PC screens are clear even in quite bright environments.
Some good points Matt. We turn the lights off in our classrooms to enhance the image on the whiteboard from the data projector but as you say, sometimes the direction of the sun through the windows makes it difficult to see. I went into the Apple Store earlier this week and bought a digital AV adaptor which sounds like what Shelly was describing. It plugs into the iPad and the other end has two ports, one for charging the iPad and the other for a HDMI cable. I actually bought it to connect my iPad to the TV at home for my kids. I did have the VGA adaptor recommended for connecting to the data projector but when I asked the guy in the Apple store what the difference was between the VGA and the digital AV adaptors he told me that the VGA is video only but you get audio with the digital AV adaptor. I can tell you the digital AV adaptor is fantastic with the TV at home. We are on holidays at present so haven't tried it on the data projector via the laptop yet. But as Matt suggested, the view may be crisper on a TV screen. Hope this helps.