Five applications for the iPhone that will help you control your computer remotely.

Air Mouse Pro (Remote / Trackpad)
Air Mouse Pro is a full-featured remote and mouse that lets you control your computer over WiFi. It can take the place of a wireless mouse, letting you move windows around your computer screen, open applications and even draw with your finger. It has a beautifully designed user interface with full- and half-screen trackpads, gyroscopic pointing, a keyboard and remote control functions. There are dedicated media buttons that can be customized and the application can even detect which programs you have open and show the appropriate keys to go along with it.
Price: $1.99

This Apple-made application is a must-have for all iPhone users. The remote enables you to wirelessly control iTunes on your computer. The application can be used to play, pause, skip, and shuffle through music and videos in your iTunes library. You can also use it to control your Apple TV and remote speakers. You will be able to view the album artwork and be able to create your own playlists within the app.
Price: free

Rowmote Pro: Remote Control for Mac and Apple TV
Control a large range of applications like Front Row, iTunes, Quicktime, DVD Player, Keynote and Powerpoint from the comfort of your couch with Rowmote Pro: Remote Control for Mac and Apple TV. The app offers wireless gesture controls over a WiFi connection so you can launch, interact with and quit apps from your iPhone. There is a full keyboard, a trackpad that supports two-finger scrolling plus virtual buttons.
Price: $4.99

Snatch: Trackpad and Remote
Snatch is a fully customizable and programmable remote control. While the user interface doesn't look quite as good as some of the other remote applications, it has some great features. Users can control programs like Front Row, Windows Media Center, EyeTV, Safari, Hulu Desktop app, Spotify and PhotoShop from the trackpad, keyboard and buttons within the app. Snatch buyers can create their own custom button layouts and share them with their friends and family. Layouts from other customers can also be downloaded from the Snatch website.
Price: $3.99

Keynote Remote
Keynote Remote is another Apple-designed remote control application. It gives you complete control over your Keynote presentations including gesture controls to advance your slide, and next slide previews on your iPhone. Speakers can also create and view personal presenter notes on their mobile device so you can control your keynote presentation and be reminded of your lines at the same time.
Price: $0.99