It's been a while since I wrote anything at LMR, so an update is due: I've been messing about with an Arduino Duemilanove that I was given for Christmas 2008. I've done all the usual things with LEDs, servos, LCDs and the like. Also spent way too much time at the Arduino forums!
But I've also been wanting to try something with a little more memory, a little more CPU power and a little more I/O. So, I bought a module with an NXP (Philips) LPC2103 chip on it. This is n ARM processor chip with 32 I/O lines, 8k of RAM and 32k of Flash ROM. It's been a much trickier thing to get started with than the Arduino, as I expected. No ready-made IDE and I/O libraries like the Arduino has! I've built a GCC compiler that targets the ARMand I'm working on the run-time start-up code in assembler.
There is indeed a very capable IDE that can be used for ARM development. I have an LPC2106 board that I successfully programmed using the Eclipse IDE (www.eclipse.org) and GCC after reading this nice tutorial (or maybe it’s more like a book since it’s 153 pages).
I can also recommend Eclipse as an IDE. You can get all the basic info that will get you started from the tutorial that jip has linked. As for an example project (with startup files and a linker script for LPC2103) check this out: