Operators offering SIM only data deals

I had an email in from a reader by the name of Mark wondering if I was aware of any vendors that do SIM only data deals.

I was initially about to start rhyming off most of the UK (and quite a few international) networks until I realised that I think almost every deal I could think off was hardware dependent. You have to buy a dongle in most cases that I can think off — even in the context of Pay As You Go.

Does anyone have any suggestions for where Mark might look — principally in the UK?