I can whole-heartedly recommend Imaging Insurance. My annual premium works out at about £10.50 per £1000 of replacement value. But we don't pay VAT when we calculate the replacement values, so that translates into a little over £9 per year per £1000 of replacement value at shop prices (ie including VAT). The policy covers accidental damage, plus unlimited travel in Europe and up to 60 days worldwide, as well as the usual stuff. And my claims experience is very good too.
To put that in the context of the other numbers mentioned above:
ING Direct - £33.23 per year per £1000 of replacement value
Photoguard - £40.00 per year per £1000 of replacement value
If anybody else has some numbers to contribute, I'd be happy to compile them into a league table.