1. Tweetcaster - This one is great to manage multiple Twitter Accounts.
With the FREE version you do see banners ads. With the Tweetcaster Pro edition for $4.99. you can tweet with no banner ads. Tweetcaster can be used on the Android, IPhone and Blackberry platforms. This is my favorite app of all.
2. Stumble Upon on the Go is another great app to be mobile with.
This app is available on the both the Android and IPhone platforms and is used very similar as it is online. You can share, stumble and send messages the same way as you would online. If you find it slow you can change your stumbling mode in settings to make it run faster.
3. The Facebook App. The Facebook app is great for your personal account but I have not found it effective on the pages accounts on the Android. If anyone has tips on that, I'd love to know more.