I made guacamole this afternoon for a picnic our friends Wayne and Jen threw in New Jersey. It's always a hit at parties, and it's actually really easy. You just get the best, ripest avocadoes you can find, mash them up with a potato masher, and mix in chopped garlic (a few cloves, depending on your taste), onions or shallots (optional-- I usually don't bother) and cilantro (as much as you like-- also optional). Then add a generous amount of salt and lime juice—just keep tasting it till it seems right to you. Don't be shy about the salt, the avocadoes really suck it in. It's really all about good quality ingredients. Also, if you can, make it a bit ahead of time and let it sit (covered, with the plastic touching it) so the flavors can blend together.
By the way, do you know the best way to pit and slice an avocado? I learned this from Alton Brown. First, get yourself a ripe avocado. If you make a fist and feel the flesh underneath your thumb, that's about how the avocado should feel when you squeeze it (gently). Use a large chef's knife. Slice down the middle of the top of the avocado until you reach the pit. Then bring your knife around in a circle until you've cut the whole thing in half around the pit. Grab each side in one hand and twist, and it'll come right apart (if it's ripe). To remove the pit, take your knife and hack it with a bit of force into the middle of the pit. Twist the knife and the pit will come off, then pinch the knife and push down on the pit to remove it from the knife blade. To remove the flesh from the skin, score the flesh into cubes-- just carve a grid into the avocado flesh with your knife. Remove any brown spots with your knife. Then use a spoon to scoop the cubes right into your bowl.
Serve with tortilla chips.