Aviation Weather from the aviationweather.gov folks.
Fltplan.com has an app if you use their service.
FlightTools and Aviation Calculations - two decent E6B type replacements plus a bit more.
I've also been experimenting with Avilution's pay-for apps - GPS flight mapping, AFD, etc. - mostly with an eye toward whether I pick up an iPad or Android tablet this spring.
Not necessarily Android-specific but there are multiple versions of the AIM and FARs at good prices, some of them Kindle-compatible (there is a Kindle for Android app)