Kev - if you listen to pocket music players regularly, it's also worth investing in a decent set of earphones - noise isolation is key to hearing wtf is going on when 50 cars come flying past at race pace (50 Audis would be OK I guess....)
I use Westone UM1's for when I'm playing with the band, for my in ear monitors - and I can confirm that they will block out the worlds loudest drummer at 5 ft away.....
Otherwise, Sony do some cheap isolating earphones which are pretty good performers, and Sennheisers CX300's aren't too expensive either.
Hope this helps.