Originally Posted by texun Mash them up with a little garlic salt and lime juice ... yum, I want some.
I have to agree with this, although there is nothing wrong with a more elaborate concoction.
All you really need is Avocado, lime juice, cilantro, a little finely diced shallot or red onion and salt+pepper. A little diced tomato is nice for colour, but not so much that it affects the overall flavour of the avocado (finely diced red pepper would work very well here).
After that, if you want to get a little creative, go for it! Fruit pulp, such as mango or guava is a nice touch, or any of the many sugestions in this thread. I've even heard of putting diced cucumber in it... would add a nice crunch, I suppose.
As far as sour cream or mayo, I've always considered these to be 'extenders', they make the avocado go farther, but at the expense of the avocado flavour. Many people may prefer a more mellow guacamole, though, so follow your taste.