cuts of beef:

What I use in:

Beef stew, beef noodle soup--chuck

Stir fry--flank, top round (something labeled London broil, which is not actually a cut)

Fajitas--flank

Pot roast--chuck

Shredded beef for tacos, etc--shoulder blade roast (from chuck) or top round

Ribs--short ribs or back ribs

Burgers, meatballs, meat sauces--ground beef

Plain ol' steak--all the short loins are the best, and most expensive.  I don't really like to cook sirloin, but it's a cheaper alternative.

steak:

I was going to write this long entry, but I found a site that has many of the same tips I've learned (e.g., let meat come to room temperature before cooking, use tongs, don't move it for the first couple minutes so it doesn't stick).  Good stuff.  It also has all the cuts of steak so you know what you're getting.  Another good resource is Bon Appetit's "Grilling Issue."  The next entry will be about the "other" steaks/cuts of beef and what I use for various types of dishes.

Cooking the Perfect Steak