I didn’t rate any of the pre-installed apps. Of those, I use Mail, Weather, Safari, App Store, iTunes, Remote, and Calculator the most.

These are my favorites so far:

• OmniFocus ($19.99): To do list manager; best if you have the computer desktop application that goes with it; this program is the reason I bought the iPod Touch
• Facebook (free): Very well executed
• Pandora (free): Streaming internet radio that learns your musical tastes and helps you find new music
• Weatherbug (free): Quick access to satellite weather maps, video news, and local weather cams
• AirSharing ($6.99): Lets you wireless connect and store/retrieve files on your device; there are now free alternatives to this program, but this particular app still remains very popular
• Bible (free): There are several free Bible apps available; but the one called simply “Bible” (its icon, confusingly, says “Holy Bible”) is the best, in my opinion; it can download multiple versions for offline use, unlike some of the others
• A Free Level (free): Mainly because it’s so cool; but it’s useful too.
• Easy Relax Ultimate (99¢): Relax or fall asleep to your own choice of sound effects, which can be combined in various ways; for example, I made one called “Campfire on the prairie” which has the sound of a crackling fire, faint insect noises, and the occasional howling coyote; there are many built-in sounds to choose from; there is also a free version with fewer options
• Seismometer (free): A great app to show off what your device can do
• Night Stand (free): Probably the best clock available
• Dice (free): Useful if you play dice-based table games, but it’s also a great show-off application, with 3D dice that roll around when you shake the device
• Enigmo ($1.99): A fun problem-solving game, where you try to get drops of water/goo/lava to fall into the right containers
• Amazing Sudoku ($1.99): This was free when I got it; and it’s by far the best of the sudoku games that I’ve tried
• Quadrum (?): This is a fun game where you slide letter squares around to make as many words as you can; unfortunately it seems to have vanished from the catalog of apps
• Wurdle ($1.99): This one is so fun, it is almost too fun: You have a grid of letters, and the object is to find as many words as you can before time runs out (there is also untimed play); at the end of the game you can see all the words you missed; great way to expand your vocabulary!
• Sol: Daylight Clock (99¢): Visually shows sunrise, sunset, and current light/dark conditions, along with actual times; contains a built-in database, so does not require internet
• Google Earth (free): Provides most of the functionality of the free desktop app of the same name
• a2z Pro Unit Converter (free): Does every kind of conversion imaginable, and you can download more from an online, user-contributed library; some of the conversions include angles, area, blood sugar, currency, data, distance, energy, length, pressure, speed, temperature, time, volume, weight, biblical weights (find out how many shekels you weigh!), cooking volumes, biblical lengths

Honorable mention (some of these are free, some are not):

• WritingPad: Replacement for the notes app; uses an incredible input method that is so much faster than Apple’s; I wish Apple would hire this guy and incorporate his method into the basic device functions!
• EasyWriter: Landscape typewriter for email
• MobileFiles: Access your MobileMe/iDisk files
• Bookmarks: Del.icio.us bookmarks
• WebMessenger: Chat with friends on AIM, MSN, Yahoo, GoogleTalk, Jabber (there is also a free web-based app at iphone.iloveim.com that seems to work well; access it via Safari on your device)
• MySpace: Works OK, but I don’t really care for MySpace anymore
• WiFinder: Find local wifi networks
• Pianist: Play the piano
• Guitar: Play the guitar
• Brushes: Paint
• Scribble: Draw
• Swatch: Match colors; useful if you need to find something of a particular color in a clothing store, for example
• Backgrounds: Download wallpaper for your device
• Bible Reader: Another Bible app
• Stanza: Download free literature from multiple online resources, including Project Gutenberg
• Mines: Pretty much like the ol’ MS classic, Minesweeper
• MasterBrain: MasterMind-like game, where you try to deduce a series of colored pieces
• Koi Pond: Not a game, not a productivity app … but it’s pretty!
• Sunlight: See where it’s light, where it’s dark, around the world
• iTip: Calculate tips and how to split the cost of meal
• 1Password: Securely stores passwords and other information