For $10-25, you'll have the most foolproof way to ensure that the meat you cook is done to how you (and the people you're feeding) like it. It's simply the most reliable way to get meat right.

Here are the temperatures to aim for. If you're going to let the meat rest before serving it (which is a good idea), take it out 3F (single pieces of meat) to 5F (roasts and whole birds) cooler than the temps listed below:

Pork
slightly pink: 150F

Poultry (chicken, turkey, cornish hen)
160F

Beef
rare: 125F-130F
medium-rare: 130F-135F
medium: 135F-150F

Lamb
rare: 125F
medium-rare: 130F
medium: 135F

Duck
Whole duck: 170F in the thigh
Breasts:
rare: 130F
medium-rare: 135F
medium: 140F

Sausages and ground meat:
170F

Note that trichinosis (which used to be danger with under-cooked pork) is killed at 137F. Salmonella is killed at 160F. If you're worried about salmonella, cook everything to 160F.