The "best" is very subjective. Personally I like white wine with most cheeses, however different cheeses work with different wines. There are always nice bottles from every country under $20, but in that price range consistency year over year from a single producer is tough. Clearly you would be hard pressed to find a good bottle of bordeaux in that price range, but in the Rhone area there are several and even a few from Burgundy.
A few suggestions that are under or "around" the $20 price range include:
-Domaine Jean-Philippe Janoueix Chateau Croix Mouton 2005 Bordeaux
-Joseph Droughin Laforet Bourgogne 2005 Pinot Noir
-Jean Luc Colombo 2006 Cotes du Rhone La Redonne
Hope that helps.
Cheers.... Steve (The Wine Snob)