Jake you got me, I thought and thought and besides the nut and bolts only thing is maybe rivets. I am not that much into cold connections either.
warren
http://www.metalrecipes.com

Cold constructions are everywhere. It's more of a matter of realising what they are. Ways of joining materials without welding. Some of them are famous and quite necessary. What connects a pulley to a shaft? A key-way. What prevent the pulley from coming off? a split ring Have you ever telescoped two pieces of tubing or assembled a modern tent?
Have you ever stood in an old barn and admired the connections? mortise and tendon joints. Could be pinned too. Take a look at a fingernail clipper, what holds the handle on? What holds your wife's diamond in her ring? Prongs and their shape. Realise that your can of, well just about anything, is held together by a bezel of metal rolled over another shape of metal. Have you ever assembled a section of metal duct work? Or picked up a five gallon bucket and wondered how they make the wire handle stay on? Some are are more commonly seen on antiques. That wood burning stove had metal hole covers that needed to be moved. The solution was one handle that was used to lift the covers. The doors to your house would fall off if it weren't for the cold connection pin in the hinge. The spring on my screen door makes a flexible cold connection at each end. The wind shield wipers on my truck aren't welded on or even screwed on. What keeps the lid on that bucket of popcorn you have leftover from Christmas? What holds your Twisto-Flex watchband together? What keeps the hammerhead on your hammer? What keeps the handle on the end of the rope you pull to start your lawn mower? What keeps one of those pull chains on a ceiling fan together. What keeps your keys on a key chain? HMMM Brad

Here's another one - staples!
You most often see them in old repairs, but I've also seen people use staples in modern pieces, both discreetly as a convenient cold fixing, and boldly, used as a design feature.

Will

hmmmm...how 'bout
a collar with a wedge.

Mortise and Tenon is another way of joining, with or without a wedge to hold it in when done. Much woodwork is done this way, with a wedge into a slot in the tenon. Collars are a traditionally blacksmith way of joining metal work that runs next to each other.

Rick Crawford at Smoky Forge

Jake-
Another thought is using adhesives. Not particularly traditional, but gives lots of options when you want to join materials in a blind joint, or when you don't want (or can't have) fasteners visible. In a former life I did research into hi-tech adhesives for fastening metals and other substrates. From a strictly technical point of view, adhesives offer a lot of advantages over more traditional fasteners.
Rob