Kef LS 50's What Sub?

I am considering KEF LS50 monitors and looking for ideas for a sub that would be a good match. Thanks for your opinions.
Depends on how you intend on running the monitors: full range or high passed. That decision should probably be determined by how loud you intend on driving the monitors and how much bass is in the source material. Independent measurements show the LS50's distortion rising very rapidly below 400 Hz reaching about 10% at 100 Hz and 31% at 50 Hz.
thanks for the info.