Top of the range stoves (rather than woodburners) are Jotul and Morso.
Jotul claim that their stoves are able to burn methanes in the flue gas
particularly efficently - and that the effect is to release less
greenhouse gases than if the wood was left to rot. A friend showed me a
scheme the French governent was running to subsidise this type of stove
because of it's green credentials.

There is one brand of stoves from the US that uses a catalyst (can't
remember the name), but more than one person has told me they're
problematic.

I've got a Jotul F600 and recommend it - though with hindsight I would
have paid a little extra for the enamel finish.