For some reason my WiFi on my MacBook keeps flaking out and I have to disconnect and reconnect to the access point to restore the connection. I managed to write a simple shell script to do this, and I can run the script easily with QuickSilver or through Spotlight.

First do the following to create a symlink to the airport binary, which lets you control AirPort from the command line/terminal.

sudo ln -s /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport /usr/sbin/airport

Next, open TextEdit and insert the following:

#!/bin/bash
sudo airport -z
sudo airport --associate=SSID --bssid=SSID --password=PASSWORD

Save that in your home directory; I call mine toggleap.

Finally, open Terminal and execute:

chmod +x toggleap