If you use Ubuntu, you can install
gcc-4.x-arm-linux-gnueabihf if you have an ARM with hardfloat, or
gcc-4.x-arm-linux-gnueabi if without. For AVR, there is
gcc-avr. These pull in the other necessary packages. I'm sure similar packages are available on just about all Linux distributions.
Why do I suggest a C compiler when you asked about learning assembly? Because writing a bit of C code, and compiling it to the corresponding assembly using the
-S flag can be very instructive. If you know C, you'll probably want to dabble with inline assembly to enhance your learning curve. Also, the above packages do install the necessary binutils too for compiling pure assembly source.
Note that the GNU toolchain uses the
AT&T syntax, not Intel syntax.
