1) Don't use WEP - no matter the password length it's only a matter of packets (time: average 5-20mins).

2) Enable your router's Wireless MAC filter. For linksys routers It's found under wireless/w mac filter.
After enabling choose the option 'Permit only PCs listed to access the wireless network'
Lastly edit the MAC filter list. Notice the Client MAC list, you should see your laptop/wireless
devices listed there. Select/add them. Make sure that you recognize the network names/MAC.
To see your MAC address on the wirless use ipconfig /all and ifconfig on unix/mac. Anything you don't recognize simply don't add. (Also take into account this is not enough on it's own, anyone with a linux/unix system can fake YOUR mac address and still use your router;)

3) Use WPA2 with AES. A lot of older devices/operating systems don't support WPA2 or have issues decrypting it.
In that case you may use WPA with AES again. Most WPA attacks are based on capturing a client's authentication
with the router and then performing a bruteforce attack using dictionaries/generated dictionaries.

4) Set a strong password using http://www.pctools.com/guides/password/

You should be all set. I would recommend using all 64 available characters and then just saving that on a file.
use a USB device to copy it/add it to all your devices. (Or altenatively copy while on the old encryption;)
This doesn't mean you're secure from other forms of attacks. Use a firewall and a smart malware detection system.