Royalties from stuff you've shot is a good way to make money, or extra money. Chances are you have a ton of footage that other people can use too. So, why not make a stock footage reel and send it off to some of the various companies that sell footage? With enough stock footage you can pretty much put together a whole production and never pick up a camera.
The key is quality and resolution. Stock footage companies want the best quality and high resolution. Don't worry just yet about HD footage, companies still buy and sell SD footage. Look through some of what you have, export it at NTSC 720x486 - 29.97 (30) FPS, DV-AVI to a mini DV or DVD and pitch it to some companies. You may get a few hits! If you have HD footage then thats even better. Hey, that footage is just collecting dust anyway, why not make a few dollars from it?
If you want to get more bang for your footage and you are willing to spend the time making discs, try putting your footage on DVD and selling it yourself on eBay. This way you keep all the money. I've bought plenty of discs off eBay and so have others. You can even go shoot footage just to sell yourself! Videographers are always looking for fresh new footage. And the less they have to pay a crew to go get that footage saves them money.
A few years ago I put out a disc of backgrounds called "Screens". I marketed it myself and sold via the web and eBay. I sold to the Navy, Boeing, various production companies and companies with their own in-house facilities. At that time hardly anyone was producing background screens for software so the product was a hit. Today it's much easier to get a disc out and sell it. Cafepress, Lulu and Amazon all have facilities to produce CD's and DVD's. You can open your own storefront and sell your footage!
Don't stop at Stock Footage. Voiceovers, graphics, animations and other elements are also great products. If you have the talent and creativity, go for it. make some cool stuff others can use!
I am currently working on a disc of Lower Thirds. Stuff I can't find anywhere else. And don't forget the "Home Movie market", more and more folks are making their own home movies using NLE's on their PC. They want snazzy graphics and footage too! Will you get rich? Probably not, but you will supplement your income, and extra money is always welcome in my viewfinder!