It's amazing for me how many people don't have a secured wireless internet or for that matter, a weakly secured one. If you take your blackberry out or anything else that has wireless and go down a residential street, or for me, an apartment complex you'll see that many of them are completely open and you can "steal" their internet. So in this post I'll tell you how to secure your wireless modem or router so people wont have access to it.
In many routers you there are options of different types of security available. They range from hiding your SSID (the name of your router) and WEP to WPA or WPA2 encryption.
The first two are not really securing your router as it's very easy to detect hidden wireless and takes only about 10 minutes or so to hack into. You can see youtube videos and download programs to be able to this very easily.
WPA and WPA2, however are the best type of encryption you can use today. WPA2 if possible would be the optimal choice as it corrects all of the flaws of WPA. Every newer devices allow for WPA encryption, and similarly many of those are allowing for WPA2 encryption. You'll want to select a very good password as well. I would suggest a long password as you'll only have to enter it once per device. If you have trouble thinking of one, I recommend using a website like good password to create a good long one for you that has both lower case and uppercase letters, numbers, and special characters.
Lastly, if you are so technically inclined, I recommend you upgrading your router (if possible) to something like DD-WRT. This is a firmware upgrade that will literally turn the functions of your router into a $300+ router. I can't highly recommend it enough. There are also other things you could do, like MAC filtering, etc. This doesn't really qualify as securing your wireless, but it is another security feature. Similarly, you should have it set as a DHCP server to help fight off any hackers from the internet along with the built in firewall.