I've got one of those. I picked mine up at Staples for around $90. As I recall, it's manufactured by APC (unfortunately it's at home and I'm at work so I can't look at it).

Ah, here we go: http://www.kk.org/cooltools/archives/001641.php

I'm very happy with it. I used it on an SFO/HKG flight to watch a couple of movies on my laptop. I didn't come close to exhausting available power.

It has an indicator light showing approximate charge, an on-off switch and a cable that allows it to be used while it's charging. It comes with a variety of tips for different laptops and, as I recall, either has built-in USB ports or an adapter that will let you run USB devices from it.

Well worth the money, in my opinion. I bought it went the extended life battery for my Sony VAIO died. Rather than spending $300 for the battery and, in a couple of years, adding it to my collection of accessories that are now obsolete because I bought a new machine, the APC device works perfectly. It also makes a nice heat shield if you're using your laptop on your lap.