Ok, here goes (lot's O research behind this one....)

For a real dull shine or marks/marrs from boat covers, tie-down straps, etc - Meguires #44  (available at Boater's World).

For follow-up on the above, or to just remove minor scratches/swirls - Meguires Paint Cleaner (most automotive places carry it)

To really bring out the shine after using the above products (in order) - Meguires polish  (again, most automotive places carry it)

Finally, use 303 Aerospace Protectant to bring out that deep, "wet" look and protect it from UV rays.  Yes, it's a wax-like product.  No, don't apply it over a wax - it needs to bond to the paint.  No, don't apply a wax over it, it's just over-kill.

Cool thing about 303 is that you can use it on vinyl, plexiglass, trim -- even your tires.  You can get 303 at Boater's World, but save your $$ and buy direct: http://www.303products.com/main.php?infopage=protectant It's about 1/2 the cost.  BTW, I've been trying some of their other products and really like them so far.

Oh!  For plexiglass, use Meguires plexiglass polish/cleaner - awesome stuff.  Buffs out the marks from the cover as well as minor scratches.  I found it at Boater's World.

In-between, wipe down with Meguires detail spray.  Just be sure to use it in the shade or else it will streak.

Personally, as soon as I pull the boat out of the water, I wipe all the water at the boat launch, the follow up with the detailer later when it's in the garage.

A good shop vac takes care of the carpet too.  Speaking of which, Goop does a good job of taking out the grease and stains.

Need more tips?  Check out http://www.bassresource.com/features/BoatFinish.html , http://www.bassresource.com/features/bass_boat_maintenance.html , and http://www.bassresource.com/features/boat_cleaning.html

I know, self promotion.  But really, they're good articles.

Hope that helps!