Finding design inspiration

Pttrns.com

Pttrns.com exhibits collections of screenshots from well-designed apps, tagged by use case. For example, messaging views for Android:

UI OH MY

UI OH MY is another site featuring examples of successful app designs.

Download similar apps

Download highly-rated apps that are similar to your app. Try to find something that looks good and mimic it--imitation is the sincerest form of flattery.