But it can be simplified a bit. Basically, there are two kinds of waterproof-breathable materials out there: Membranes, and coated fabrics. Membranes are themselves waterproof (Gore-Tex is a membrane), without any modification. Coated fabrics are just garden-variety fabrics of one sort or another, with a coating (usually polyurethane-based) that has a microscopic structure which allows water vapor generated by the wearer to escape, while keeping rain water out. One confusing thing is that coated fabrics sometimes are used like a membrane - that is, sandwiched between two other fabric layers the way Gore-Tex is in three-ply construction.
You also can break things down this way: As a general rule, all the Xalt's and H2NO's and Triplepoints of the world do a pretty good job, but don't breathe quite as well as Gore-Tex. On the other hand, they're cheaper, breathe pretty well, and in some instances - particularly if the face fabric on the outside of the garment is very wet - may perform better. About all you can go on are generalities and personal impressions. There simply is not a single standard - at least, one that everyone agrees on - that measures the waterproof-breathable qualities of the many fabrics out there.
That said, a few recommendations: Kokatat's Lite Wave Drytop ($314) is a high-quality Gore-Tex piece that you just won't be sorry you got, although it is a bit pricey. Rapidstyle's Cataract top ($185) uses a coated fabric for a jacket that performs well at a considerably lower price than a Gore-Tex piece. At an in-between price, Stohlquist makes a basic top called the Contour that uses Gore-Tex and costs just $200.