When good performance needs to be reconciled with limited size, 2.1 Hi-Fi audio is a safe bet. The satellite speakers are small enough to fit on either side of a PC monitor and subwoofer, under a desk or stashed in another space with limited room.
Of course, a 2.1 system only reproduces stereo. You won't be able to get the benefit of 5.1 surround sound, for example. Remember, however, that music is still almost exclusively in stereo. So it's really only an issue for DVDs and games where surround sound is a real plus. There are, however, 3D-sound simulation systems which, while they can't really compete with a true surround system, can improve results. Today, multimedia 2.1 systems have gotten a lot better and offer real quality sound reproduction at a really accessible price. For this comparison, we've looked at and listened to new 2.1 systems priced at under $100.