Pandora.....these are, with Troll, the most well known of these things. heres the link for the UK
http://www.pandora-jewelry.com/UK.aspx and the US http://www.pandora-jewelry.com/US.aspx The Pandora system is quite different to the Troll system as it has a screw thread with which you attatch your beads however the beads can be used with other bracelets and visa versa, just be careful and check. The bracelets are about £55.
I haven't got any Pandora beads but that doesn't mean I wouldn't include any in my collection. So I won't say much more as I like to speak from experience.
If you google or ebay search "Pandora bead" you are likely to receive the most good hits