There's an M-Audio 2.1 system on Amazon for about £149 that looks decent...
M-audio isn't bad, but the budget end are really more of a convenience product than hi-fi..
similar to logitech , although obvious m-audio speakers are usually PHYSICALLY much bigger, and therefore have much bigger sound.
I've seen klipsch RB-10 on sale recently for $70 at newegg.com
and there's also pioneer bs 22 for ~$50 sometimes..
Pair it with ANY $100 stereo receiver (used or new) and it's going to blow away most 2.1 convenience products.
Optical input is really important because the computer is very noise polluted.
galvanic isolated usb is the same as optical, because it uses an optical coupler chip.