Tripods are one of those
very useful things in photography. Whether it's supporting a telephoto lens or helping you take long-exposure shots, or even self-portraits, it's pretty safe to assume that almost everyone will wind up with a tripod at one time or another. (Even if it is the
$1 image stabilization device 
).
There are two main categories of tripod heads out there (I'm going to leave out the really specialized things like the tracking heads, etc): Ball heads and pan/tilt heads.
Pan/tilt tripods are really common. They look something like this:
Ball heads are also available. I've even found them on tiny table-top tripods. They look something more like this:
Now, which head you prefer depends on preferences and also what kind of shots you take. If you're trying to do a lot of panning, a ball head probably won't be as easy to use. But if you're looking to move your camera quickly to different positions, a ball head may be faster. There have been lots of write-ups about which is "better", so I'll leave you with a few of those articles:
So, this week's question is: which kind of tripod head do you prefer? And if you like your tripod, why not share with us the type you have any why you like it?