I got some of the spark plugs others have mentioned from ebay. I think it was about 50 pairs for 7 quid and they are brilliant. One of the guys i work with now also uses them as does my dad. for me they drown out everything but high pitched sounds (fire alarms, phone etc).
I struggle to get to sleep if i can hear anything as i just concentrate on it, unfortunatly that means clocks and the wifes snoring. Plugs go in, i stay asleep until the alarm goes off in the morning.
My mum said she had tried a pair but that they didn't work, i looked at her a bit funny and asked how she put it in and she had just literally tried to push it into her ear ><. You gosta roll 'em!