After Tracey Cox Supersex Toner Balls

I've been using the Tracey Cox Supersex Toner Balls and want to step up to something more challenging. Any suggestions from you guys?

Many thanks,

LuLu

These have just been released from Lelo http://www.lovehoney.co.uk/product.cfm?p=25627 a mini version of their beads - I'm gonna get them when I have the money, as mine seem to be doing nothing.