It's the rare notebook that doesn't have Wi-Fi, but not all models offer Bluetooth. Though not a critical feature, the short-range wireless technology is handy to have for things like cordless mice and cell-phone tethering (i.e., using your phone as a modem). Meritline has a teeny-tiny USB-powered Bluetooth adapter on sale for just $7.99 shipped.
What I love about this thing is that it's so teeny-tiny: Just a rounded little nub. You can leave it plugged into a USB port and barely know it's there. This is a Bluetooth 1.2-compliant adapter with a listed range of up to 65 feet (though let's be honest: 30 feet is usually where Bluetooth tops out).
I really love using a Bluetooth mouse when I travel, and on the rare occasions when I need to tether my Palm Centro, I can do so without a cable. For 8 bucks shipped, there's no cheaper (or less obtrusive) way to add Bluetooth to a notebook (or desktop, if that's your thing).