I have compiled an Eclipse project that contains all the Arduino core core (currently based on Arduino version 0022) a small subset of third party libraries and my own libraries. Of course you can add other libraries to this project. Modifications must be done to the file paths of #include directives, since we cannot rely any more on the magic done by the Arduino IDE.

Download my latest Arduino Eclipse Framework project

and unzip into your Eclipse workspace directory. Then import the Existing Eclipse Project de.grapelabs.arduino.framework.

There are some build configurations defined, all with a crystal clock 16 MHz. You can define more build configurations as needed. 

Choose for example the atmega168_16000000 configuration and compile the project. You should get a libarduino.a file in the atmega168_16000000 subdirectory.