In terms of the big fridge/freezer models, what's the largest one that's the best value?
You don't say how much room you have. What width are you talking about? What's your budget? In any case, check out the Frigidaire/Electrolux twins (i.e. all-fridge all-freezer units). I'll link to a thread which has several pics.
Here is a link that might be useful: Thread about Frigidaire/Electrolux Twins