Tapping knowledge gained in the first class I took at JWU, Stocks and Sauces, this is pretty much all you need to know.
First of all, the basic cream sauce is whats called Béchamel, its refered to as one of the 5 mother sauces (along with Velouté, Espagnole, Hollandaise/Mayonaise and Vinaigrette) because they are the bases for just about every other sauce you can think of.
Béchamel
1 cup milk
2 TBSP metled butter/Flour
salt/pepper/nutmeg to taste
Cook the melted butter and flour for about 4-5 minutes. In the meantime heat the milk and then add it to the roux (flour/butter mixture) and simmer over medium heat for 15 minutes until thickened (this will be a medium consistency, less/more roux would change that)
From that you can do:
Standard Cheese Sauce
Béchamel + grated cheddar cheese (better than the powdered stuff in packets or the crap in jars and too easy to make)
Mornay Sauce
Béchamel + Gruyere and Parmesan Cheese + heavy cream (best "white" mac+cheese ever..)
Curry Sauce
Béchamel + 1 tsp curry powder (excellent chicken or rice)
Sauce Soubise (aka onion sauce)
Béchamel + Onions (sauteed and pureed) + heavy cream
Aurore Sauce
Béchamel + 1tbsp tomato paste (good with fish)
Sauce Albert (aka Horseradish Sauce)
Béchamel + grated horseradish + white wine + cayenne pepper + heavy cream (good with beef, but its not Arby's Horsey Sauce)