CSS Bubble Tooltips
This example will show you how well this tooltip stretches for long descriptions when you hover here!WWOOWW!,
This really is a very long tooltip. Normally they aren't this long but every once in a while you feel the urge to use a really long description to make sure you get your point across to everyone! This could go on and on all of the way down the page and probably overflow onto the next website you visit! No, seriously go check the next website you planned on visiting..but you have to be quick when you move the mouse off of this link. I bet you can't do it fast enough ;). Also with the IE hack for the :hover state, you can do this with elements besides anchors.
If you dont like how it allows you to hover over the tooltip also then you can adjust the padding and top to separate the tool tip from the link.