I really like this one:
http://events.nytimes.com/recipes/11473/2008/04/20/Baked-Sea-Bass-Stuffed-With-Shellfish/recipe.html

easy and impressive. Never had it fail!

oh sorry we made this one - it is VERY good and VERY easy:

http://www.food52.com/recipes/2462_whole_baked_fish_in_sea_salt_with_parsley_gremolata

MariaRaynal and I did the whole salt crusted fish referenced above - neither one of us had done it before but it came out great the first time - also it's FUN - you could let everyone have a shot at bashing the salt and getting the fish out - think fish pinata! (we were timid on our first try and the bashing tool bounced right off which was hilarious!)

Don't give up on your 'whole fish' idea if you are fairly comfortable already with cooking fish for yourself and have a decent sense of what 'doneness' looks like.

Salt crust is a little more intimidating to try first time on guests since you can't see or touch it. I've done this one a few times and it's fantastic. I had no trouble with the outcome and it looks beautiful.

Whole Roasted Arctic Char with Fennel and Pistou Recipe : Tyler Florence : Food Network http://bit.ly/f4Wx4G

I'm with mrslarkin. Just eat it straight out of the packet.

The en papillote is a great idea! Here's how I do it: http://www.food52.com/recipes/4583_salmon_en_papillote Plate each packet - I'd just eat right out of it, especially if you include veggies in there too.

But would they poo poo the fish if they are not fish fans??

May I suggest fillets instead of a whole fish, cooked by the slow roast method in A New Way to Cook?

Heat the oven to 275. Oil a baking pan that will hold the fillets in one layer. I thin slice lemons and put a layer of lemon down, topped by thyme sprigs. Put the fish skin side down on top of the thyme sprigs. Drizzle with olive oil. Salt and pepper and put some additional thyme sprigs on top. Put in the oven for 15 to 30 minutes, depending upon the thickness of the fillets. Don't go by the appearance. Test to see when they first get flakey in the middle. I promise, they will be silky and delicious.

Actually, a quick follow-up question to hardlikearmour: If all the guests have little packages on their plates, pull the string to reveal the succulent fish inside...then what do they do with the paper? Do they slide it all off onto a plate and then I circulate a discard-dish?

Yes! Individual little papillotes would be lovely - and all made in advance! Thanks for your response and suggestions.

It would make a great presentation for sure. Here is a recipe that has instructions for 8-10 servings: http://www.epicurious.com/recipes/food/views/Whole-Fish-Baked-in-Sea-Salt-241114
I'd also think about en papillote as far as presentation. Everyone gets their own little package to open, and you can assemble them ahead of time.
Good luck! I hope your dinner is a smashing success.