IMO, the most important thing every dog should know is a reliable recall (come). This is something that could very well save a dog's life. If a dog ever gets loose, the leash breaks, the fence isn't as secure as you thought, a solid recall would bring the dog back to you instead of him/her running into the street and being hit by a car. Second would be a drop-it or leave-it command. Again, this could save his life by allowing you to remove an object they shouldn't have like glass, poison, a stray cat... Third would be a reliable stay/wait. No one wants to worry about their dog bolting out the door everytime it's opened. After these, walking politely on leash, sit, and down.
"Violet" UAG1 URO1 UWPS UGWPCH UCD CH AA's Ultra-Violet CD CGC TDI (working), ABIMBS, Multi ARBIMBS, Multi MWP/MWPP, HIT (Agility), 2x Obed Total Dog, 1x WP Total Dog, UKC Super Dog #60, 2010 Weight Pull All Star... and more to come.