i make my gravy with meat drippings and the fond deglazed from a pan, added to a roux (equal parts of flour cooked in butter) and meat stock, if i have any available. if not, beef bouillon. if you want to sweeten it up a little, blend in some cooked carrots.
my mil used to swear by something called gravy master, which was some kind of concentrate, but i thought it tasted funny, kinda plastic.
i have started to make my own stocks, saving things like veal bones from a dinner i made the other night, or the water leftover from boiling lobsters.
the veal and other beef bones and trimmings are browned, then coverd with water and boiled/simmered with some herbs for the beef stock.
for fish stock, i start with the lobster water, and add shrimp shells and fish bones and boil them down.