A few of the popular ones I see mentioned on here are: Aaduki, PhotoGuard, E&L and Glover & Howe. I've heard more bad stuff aout E&L than any of the others and for that reason, I chose to avoid them. People rate the others pretty well. I'm with Glover & Howe but have thankfully not yet had to claim. What I have heard about them is that the claim process was fairly painless.
The prices between the companies varies, but that was not what influenced my decision. I downloaded and carefully read the small print/T&Cs for each of them and decided on that basis. Some companies for example might not cover theft from a hatchback. Others do, provided that the equipment is out of sight. Photoguard I found has quite strict guidelines on home security, so it's worth checking that you meet the requirements.
It's worth mentioning that you may also get cover on your existing home insurance but in my experience the level of cover per individual item wasn't sufficient to cover my gear i.e. it only went up to £600 or so.
HTH