sidenote: Most of these apps are probably made for droid as well, do a little search and see what you can find.
MobileRSS - A great app you can sync your google reader too. This is helpful for slow days at work.. or anywhere you feel the need to catch up on your blog reading.
Tumblr gear - If you're into tumblr, this is by far the best app for browsing through posts. It loads super quick and also makes it easy to "like" and "reblog".
Sparkpeople - This is SUCH (!!) a great one. I think i'm long overdue for a lengthy post about my love for sparkpeople in general. Many people use it to lose weight (very successfully too) but I use this to track my food intake to make sure i'm getting enough protein/fats/ect. You can ANY food and also add entire recipes to see how many calories/fat/protein/vitamins in is each serving. That's just the beginning. I love sparkpeople.. and having it wherever you go is very convenient.
Craiglist - Pretty self-explanatory. I found my couch and bed while waiting in line somewhere.. hows that for convenient.
Yard sale mapper - This app takes all the garage sale listings from craigslist and puts them on a map. Makes it so easy to map out your route and get directions to each one. (You can also view the craigslist listing to see what they were advertising..)
ThriftBuddy - A thrift store mapper that finds any/all thrift stores near your location. Perfect if you're traveling..
PuddingCamera - Another awesome free photo app. It's mostly in korean but still pretty easy to use. You can choose different films and cameras... endless fun.
Fooducate - You can use this app to help read ingredient lists and nutrition labels on food. It tells you other words used for MSG, preservatives, ect.. and if its bad, it shows you a better option for the same type of food. Confusing? Try it out, it'll make more sense.
Pinterest - So glad they made an iphone app! This is just as addicting as the website.
Firefox home - This gives you access to your desktop history, bookmarks and open
tabs on your iPhone. If you're like me and have about a million websites bookmarked on your computer but not on your phone, this one is for you. I love being able to bookmark a recipe on my computer and pull it up on my phone at someone elses house later on..
MapMyRun - By far one of my most favorites.. this makes running so easy (well.. not literally). It tracks your pace, distance, and route using GPS, which makes it easy to hit your goals. I LOVE it.
Some basic ones i use all the time are: twitter, urbanspoon, yelp, pandora, paypal, netflix, and Skype.
And since i'm always looking for new ones, What are your top 3 favorite apps?