You can flash various wifi access points with openwrt. From then on you can even customize the device with packages you want. Like for instance a small http daemon or such.
Here we have the Linksys NSLU2 wich has it’s own “homebrew” firmware available at nslu2-linux.org. With this you can turn your small low cost storage device into a small linuxcomputer.
These are the ones I know about… If you know other, feel free to post them in the comments section.