Linksys WRT54GL in Client Mode + AP Mode
Linksys WRT54GL is great. It has a good chip. Runs Linux.
First, Install OpenWrt Kamikaze.
Then you simple need to configure /etc/config/network and /etc/config/wireless to fit your needs.
Check my sample config files at http://if.tehif.eu/config/openwrt/.
Use network.txt if you need dynamic IP config, otherwise network.static.txt if you need a static IP configuration.
And wireless.txt is configured to connect to remote AP which uses WEP for encryption, and to broadcast local using WPA2.
Look at my samples. Edit them for your needs. Enjoy.
You can buy a directional Antenna and replace one of the defaults.
This is a typical case if you cracked a neighbour's Wifi and you want to have a good signal all over your place.