Facebook Keep an eye on your company or organization's page on Facebook. Reply to comments, manage status updates and upload images.
VideoUp VideoUp makes it easy to upload videos to your Facebook profile. This only works with the iPhone 3GS currently.
Sync.ME - Social Contact Sync Sync your Facebook friends to your phone's contact list. It won't overwrite your existing contact pictures or information unless you want it to.
Twitter If you're only managing one or two Twitter accounts, the Twitter for iPhone app is perfect. The UI is intuitive. I've been using it since it was Tweetie and have no complaints - just wish I could schedule tweets through it!
HootSuite for Twitter & Facebook I love HootSuite because it lets me manage multiple twitter accounts without getting overwhelmed AND I can schedule tweets for the future, which is a must!