Back when I was just getting into networking, ethernet hubs were common, and switches were a fancy, expensive alternative. Then the price of switches came down so much that hubs became pretty much obsolete, except when you actually didn't want switching - as wikipedia points out, "hubs can still be useful in certain circumstances," such as "for inserting a protocol analyzer into a network connection." That's a particular use case I've come across several times, especially at work -- I haven't yet learned all the ins and outs of configuring RSPAN (Cisco's implementation of port mirroring) on Cisco switches, and sometimes it'd really just be easier to plug a laptop into a hub with the system I want to monitor.
The only problem is, I can't actually find any place to buy a hub. Small switches start at $25, so I'd expect to be able to find a hub even cheaper... except I can't actually find one at all. A google product search for "ethernet hub" instead finds ethernet switches and usb hubs instead, plus a few expensive ethernet devices that I'm not quite sure what they are :)
Does anybody actually make hubs anymore? Or am I going to have to hang out on ebay and hope to find someone who's getting rid of one, and who knows enough about what they're selling to describe it accurately? A gigabit-compatible hub would be ideal -- do those even exist? Wikipedia only talks about 10/100 Mbps hubs.