If you've lost the white buds that came with your iPod, then £20 is a decent price to spend on some entry-level earphones. The MX 560s from Sennheiser ring up to around just that price and they come in a range of colours, too. Do they perform decently too?
For bottom-end ear-pleasers in red, white or black, the MX 560s are affordable without being cheap. In fact, they offer better sound quality than standard iPod earphones, despite costing around the same price. Most notably, they offer good bass, along with a moderately clearer high end, resulting in a fairly powerful sound for earphones of this ilk.
Mark Knight's Party Animal, a dance track with a hard-hitting bass line, sounded meaty for a pair of £20 earphones, and a couple of steps up from what Apple's earbuds are capable of producing. The Sennheisers are already the better option.
Moving on to some good ol' rock 'n' roll -- Don't Wait by Dashboard Confessional, to be precise -- we heard fairly bright tones, with Chris Carrabba's haunting vocal harmonies more prominent and audible through the 560s than through the iPod's stock 'phones. They're not the loudest earphones on the planet, but they retain their decent clarity even at high volume.