Some of my favorite Android apps:

• Podcast Player: MortPlayer Audio Books - Free. Customizable interface. Easy to operate. Does auto-bookmarking. 10-second seek function.
• Twitter Client: TweetDeck - Supports multiple Twitter accounts.
• WolframAlpha - Amazingly powerful "computational knowledge engine". Custom soft-keyboard built into app for easy entering of numbers, math symbols, and Greek letters. (Webapp accessible at wolframalpha.com.)