As guides to collecting, I find the three Alan Hall volumes and the Kevin King book invaluable.
The three Alan Hall books are mainly pictorial with the only real text being the occasional footnote and contents list for each set. These books show the uniforms and equipment in and out of their packaging as well as displayed on figures. I did think these were still in print, but apparently they are now out of print. Modeller's Loft (Alan Hall's shop) have some left and are selling all three volumes in a bundle for £95.
If you want any Action Man books, at £95 for all three, they are still worth picking up as these are probably the definitive guides. Modeller's Loft are also saying that stocks are low.
The King book shows the gear displayed on figures, but has much more text, with hints and tips on what to look out for when buying. It also has a section on the '90s Action Man revival as well as a section on Tommy Gunn and Cherilea vehicles.
Out of print and currently fetching between £30-£50. There is one up for auction on eBay (as job lot with the dreaded Frances Baird book!) with a £8.99 opening bid and no bidders as yet.
If you want a much more detailed read and a cracking history of Action Man, then this Ian Harrison book comes highly recommended. Plenty of full colour illustrations as well. The book is out of print but there are plenty on eBay and Amazon between £12-£25. It's original price was £20, so the asking prices for it aren't bad.
Finally if you want a simply superb picture book, showing Action Man photographed in "real life" situations and settings, this almost 300 page book by NG Taylor is absolutely superb. There are a few errors, but nothing major (nowhere near the horrors of the Frances Baird book!) and completely negligible, as it is first and foremost a fun, lavishly illustrated picture book and not a definitive collectors' guide.
The book has one quirk; although it covers every period of Action Man's 1966-1984 run, all of the uniforms are photographed on painted head figures, the author's personal favourite type of figure. Out of print and going for anything between £30-£150! Well worth hunting for at a bargain price.
Finally, this is the one to
AVOID!