Necessary for certain routers

I use this antenna with the Linksys WRT54GC. Without it, my reception is essentially limited to the room the router is in. With this antenna, I get a good signal all over my house, and a weak signal outside.

It's very easy to install--just screw it in. Note that this antenna won't work with routers that don't have an input for it. That's kind of obvious, but I thought I'd mention it. Be sure your router can accept this model before buying it.