I have some books to recommend to everyone, but particularly Mal: There's an English gentleman named Peter Holland, a model maker, inventor, and draftsman, who builds the most amazingly wonderful mechanical toys and models from stuff like paper clips, balsa, styrofoam, yogurt cups, etc. I have three of his books, the title of all three is Amazing Models!, and each has a different subtitle: Rubber Band Power, Balloon Power, and Gravity Power. There are others, too, I believe. These books are chock full of the most fantastic little mechanisms: escapements and latches and spring-loaded catches and so on, with excellent drawings. Just wonderful mechanical idea books. Here are the ISBN numbers:Note: I have heard that, unfortunately, these books are out of print.Rubber Band Power: 0-8306-3220-4
Gravity Power: 0-8306-3501-7
Balloon Power: 0-8306-3230-1They're all published by TAB Books, and cost 8 dollars US. If you like building and/or thinking about mechanical stuff, you'll LOVE these books!