Knox, R.: Experiments in Astronomy for Amateurs
Long since out of print, but easily available 2nd Hand, this is far and away my favourite book on practical astronomy. It has a wealth of ideas and models to construct. There are things like sundials (of various kinds), planispheric astrolabes, eclipse predictors, and models of the solar system, all of which are constructed by simple geometrical methods. If you like making things that work and, in the process, teach you about the theory, this is the book for you.
Tonkin, Stephen: Binocular Astronomy
The physics and physiology of binocular visual astronomy is followed by an in-depth description of how to choose, test, and buy the best equipment. This is followed by details of care and use your binocular. Finally, there introductory lists of several hundred of the most exciting objects for 2-inch (50mm) and 4-inch (100mm) binoculars, complete with finder charts and descriptions.
Harrington, Philip S: Star Ware
Very useful book, now in its 4th edition, which gives an unbiassed view of commercial offerings and has a few useful projects for the "home tinkerer".
Harrison, K.M. : Astronomical Spectroscopy for Amateurs
Up-to-date practical spectroscopy book, which will enable amateur astronomers to develop the skills and equipment needed to prepare scientifically acceptable spectra data, and to make a valuable contribution to ProAm projects.
Mills, H. R. : Practical Astronomy: A User-friendly Handbook for Skywatchers
Lots of astro-gadgetry to make, from simple finders to magnetometers for aurora prediction. The author's infectious enthusiasm shines through.
Tonkin, Stephen: AstroFAQs
THE quick reference to get you up and running in practical astronomy; an enormous amount of concise, practical information.
Tonkin, Stephen: Practical Amateur Spectroscopy
For a long time this was the only complete book on amateur astronomical spectroscopy. Includes background theory and a variety of spectroscopes (and techniques) from DIY to commercial. Now supplemented by Ken Harrison's excellent work on the subject (see above).
Waugh, Albert E.: Sundials, their Theory and Construction
Easy to read with lots of ideas for various kinds of sundials.