Are you interested in just propagation or other things about the plants. I've already made that choice. Manual of Woody Landscape Plants.

Tom_w and I always seem to disagree on Dirr!

I'd choose "The Reference Manual of Woody Plant Propagation" by Dirr and Heuser (1987). I feel it is more complete and better referenced, if propagation is your primary interest (as it is mine).

You should just plunk down for both.

Shoot

Shoot,

Yeah, I know I should have both, along with a greenhouse and automatic misting system! My wife, oddly, seems to think I should ease into this activity. Perhaps she's looking at the garage full of power tools that I bought in anticipation of all the furniture I was going to build? Hey, I've made a cat bed, an aquarium stand, a printer table, a shoe rack, and a wheeled plant stand! Of course, she's waiting for the sleigh bed and bedroom set, the dining room set, the entertainment center wall unit..., but I digress. I've been a propagating dabbler since I was a kid, and am ready to get more serious about it. I understand the generalities and am ready for the specifics regarding particular species. Propagating woodies is more mysterious to me than herbaceous perennials, and, it seems, more species-specific.

At the moment, I own Bir (1992): Growing and Propagating Showy Native Woody Plants, and have on loan something like the 1975 edition of Hartmann and Kester: Plant Propagation, Principles and Practices. The former covers specific species, but only a few and only briefly, the latter is detailed, dated, and doesn't cover specific species.

Shoot,
Perhaps we do disagree, perhaps not. I think we agree that Dirr is 'Da Man'.

clibanarius,
Now that I know a little more about your interest, and that you have Hartmann and Kester, my recomendation would agree with shoot.
We are just going into one of the busy periods of the year for propagation. Find a few plants that you really like, learn about them, and get started. You should find most, if not all the information you need in the books you have, or on the internet. My point is, you do not need to know everything about all plants and methods in order to be successful at propagation. I think I agree with your wife, add tools and references as the need develops. A few used pots, some potting soil or sand, a small quantity of rooting hormone and some plastic bags and you are off and running.

If you check your local library, you may be able to check the books out, and experience them before making your choice.