Guar gum (available at most health food stores) works very well for me and adds no taste or carbs; 1 teaspoon will thicken about 1 cup of liquid. Another option would be to add some heavy cream to the pan juices (count the carbs) and cook it down until it thickens.
Flour and cornstarch are no-nos on low carb, although the Eades' (protein power) do allow flour in small amounts for things such as gravy as long as you count the carbs.