We always use http://www.atlasdirect.so.uk and have found costs to be significantly lower than TA's etc.

You should definitely not use the travel agents' insurance. Very expensive. We use Direct Travel Insurance: http://www.direct-travel.co.uk/

I used to use direct travel insurance but since they now use AIG they no longer insure for visits to Cuba so I now use Atlas direct who do.

The other thing you need to watch out for is that some insurers do not automatically cover cruises!! Atlas direct do, and their rates are more or less the best around. They also give you the option to vary the excess, and sometimes going for a zero excess (instead of £65) does not cost much more.