Here are my tips (partly summed up from others, with some additions):

- Change the default SSID to something specific
- Change the default IP address
- If you have a web-based AP interface, change the default password
- Disable SSID Broadcasting (as suggested by nabylbt)
- Enable WEP with max key, without using a passphrase (generate it manually)
- Block all but specific MAC address(es)
- Put a firewall on your internal network (if applicable) (this will protect your internal network in case you are compromised)
- Place firewalls on all wireless stations (to protect each of them from external attacks)

If you want more secure transfers, you may also want to think about using a VPN or some other form of tunneling to ensure secure transfers between all of your workstations, servers, etc.

And something you may want to think about if you have programming experience... write a program or script which will automatically generate a new WEP key after a given period of time. You can set up the script to reset the WEP key on the access point and then send you the new key either via the network (which may be unsafe) or via e-mail. My script e-mails the WEP key to me. I then have a script on my Exchange server which automatically isolates the specific message and automatically reassigns the WEP to my wireless stations. If you want to know how I did it, I have absolutely no idea... One of the women I have working for me can write scripts to do nearly anything and everything within next to no time, and she wrote these scripts for me.

Good luck

AJ