[Design, Prototyping, UI, Graphics] Androguide.fr:
Hey guys, I've recently been working hard on redesigning my app and here's a compilation of resources I found useful along the way.

Please post yours so I can add them to the OP.

Online Tools

Android Asset Studio by Roman Nurik

This is an awesome tool which allows you to generate pixel-perfect drawables for your app, directly downloadable and resized for all screen resolutions (xxhdpi/xhdpi/hdpi/mdpi/ldpi) including :

Launcher icons

Action Bar & Tab icons

Notification icons

Generic icons

Tabs icons for pre-honeycomb

Menu icons for pre-honeycomb

All icons can be created either from an image, from the provided cliparts, or even from text

An Alternative Device Frame Generator containing more devices and less strict in term of the original screenshot resolution than the official one

A very useful Nine Patch Generator

This tool is open source, too : http://code.google.com/p/android-ui-utils

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Android Action Bar Style Generator by Jeff Gilfelt

This great tool allows you to generate all the necessary resources (xml, drawables, nine patches, you name it) for your custom ActionBar theme. The Holo guidelines recommend to style the ActionBar with your branding color as an accent for example, well it's never been so easy with this tool.

You can choose the color for all the components of the ActionBar :

ActionBar color & style (solid/transparent)

Stacked Color

Popup Color

Accent Color

Contextual Action Bar background color and highlight color

Oh, and it's compatible with ActionBarSherlock, too!

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Android Holo Colors Generator by Jérôme Van Der Linden

This nifty tool allows you to generate a custom style for all the most usual UI components such as :

EditText

AutoComplete

Button

Colored Button

CheckBox

RadioButtons

Spinner

Colored Spinner

ProgressBar

SeekBar

RatingBar (normal/small/big)

Toggle

ListSelector

Fast Scroll

Switch

Just like the other Asset Studio-based tools, it generates a zipped res folder that you can directly merge into your app

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Android DPI Calculator by Martin Cohen

A very useful tool, I use it all the time. Simply input a width and/or height and it will convert it for you to all screen resolutions (even tvdpi)

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UX Metaphor Equivalents for iOS & Android by Kintek

If you're an iOS developer/designer and are converting your existing apps or making the switch to Android (or the other way around), this tool will allow you to compare both platform SDKs's native UI widgets and find the right equivalents for each component.

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Offline Tools

The Photoshop Android Design Kit by Taylor Ling : a great tool to design mockups and wireframes for you app, and now, since last update, it even includes some popular custom views such as Google Now cards, Croutons, undo-bar etc...

Custom Views & Libraries

I'm not going to make a list of all the awesome open source libraries the android community has created, this would be impossible.

But I'm going to give you links to external websites and even apps who try to achieve this goal, really go take a look, this is very inspirational :

AndroidViews.net by Nadav Fima : the name says it all. It's a website which only feature libraries related to the UI and design. My favourite of this list.

DevAppsDirect by Kenneth Lewelling : a great little app which presents many libraries and allows you to directly launch their demos, very useful to find inspiration.

The Ultimate Android Library by Alexandre Gherschon : a website AND an app showcasing many great libraries (The app is here)

This article from vogella.com : a compilation of useful open source libraries, again

Websites & Blogs

THE ANDROID DESIGN GUIDELINES : I can't stress it enough, read this twice!

AndroidUiPatterns.com : a very nice blog about android design and ux

AndroidNiceties : a blog that's basically a collection of screenshots taken from beautiful, holo-compliant (most of the time) apps. Great source of inspiration.

Romain Guy's blog : Romain Guy is an Android engineer at Google, and his blog is full of very useful articles, like these two about improving the UI performance of your app -> here & here

AndroidDevWeekly.com : a great weekly (obviously) newsletter containing cool news and links about android development/design, I highly recommend to subscribe

The official Android Engineers's blog : says it all I guess^^

Chet Haase's blog : Chet Haase is an Android engineer at Google working particularly on animations and the animation framework, his blog is full of cool infos and snippets

Cyril Mottier's blog : a great resource by a great dev, he writes very good articles and libraries and his blog contains some really awesome posts (i.e : ListView tips & trick, Android app launching made gorgeous & Pull to refresh, an anti pattern)

StylingAndroid.com : great android design blog by Mark Allison

AndroidUIUX.com by Taylor Ling : the blog maintained by the creator of the Photoshop Android Design Kit

Lucas Rocha's blog (Android dev at Firefox) : http://lucasr.org/

Videos

Android Design in Action : an awesome weekly show held by Android engineers Roman Nurik, Adam Kosh & Nick Butcher. They often do redesigns of existing apps, give many great advices. They usually focus on one specific type of apps in each episode, maybe your type of app has already been treated!

Dev Bytes : Held by Android engineer Chet Haase (and sometimes Nick Butcher), Dev Bytes is a great series of short episodes showing you how to implement some nice animations and transitions to jazz up your apps

The App Clinic : Held by Android engineers Reto Meier & Ian Ni-Lewis, this is a weekly show which takes a look at existing apps and talk about what's good and bad in their UI/UX approach

Guides

THE ANDROID DESIGN GUIDELINES (Yeah I know, but I told you, read it twice! :silly:)

The Android Designer's Cheatsheet : great all-around guide to understanding the basics of Android design (including density buckets, how ninepatches work, 48dp rule & pattern, naming conventions, etc...)