For less than £40, which is still in the budget range of speakers, you can buy a set of Sony SRS-Z510 desktop speakers. 2 way audio input enables you to plug your PC and your mp3 player in at the same time so you can enjoy 7W total output from any music source. Detachable guards enable you to choose between the industrial natural look, and the desktop look while the Mega-Bass provides you with a powerful bass sound and improved overall sound quality.
If you’ve been relying on your tower speakers and you want a little more richness from your audio then buying an inexpensive set of speakers is the way to go. Alternatively, upgrade to 5.1 or 7.1 sound card and buy a multi-channel set of surround speakers to get an even heavier, crisper, and neighbour-annoyingly loud experience. The Sony SRS-Z510 speakers offer a sensible and affordable solution.