Making a wax seal for your envelopes is pretty easy and a ton of fun if you have a couple of simple tools. All you need is sealing wax, a stamp (usually brass) with a handle, and a heat source (butane lighter works well). My source is J. Herbin, the French company owned by Clairefontaine. They've been making wax continually since the 1600's, and they have a neat product called supple wax that's flexible when hardened and can withstand going through today's mail system. I also have some custom wood handles I've been making for fun, and I'd love to get some feedback!
Link to YouTube for iPhones and full-screen viewing.