I’ve always used prosper for presentations, but someone recently put me onto beamer, and I must say I’m impressed. It lets you structure your file using standard LaTeX sectioning, and produces section-level tables of contents by default. There are 26 different themes, and an architecture for easy colour-scheme changes and so on. The documentation (beameruserguide.pdf) is a bit chatty for my taste, but pretty comprehensive: 203 pages! Very little of this is needed to use the package though — there’s a tutorial introduction, 70 pages showing the various themes, a “workflow” (only three pages, but really…) and significant repeated material (tutorial, reference, and how-to). Some of this space is also taken up with hints about presentation, most pretty accurate:

Always test your presentation. For this, you should vocalize or subvocalize your talk in a quiet environment. Typically, this will show that your talk is too long. You should then remove parts of your presentation […]

I’m currently putting together my first presentation using beamer, so I can’t really give it a solid thumbs-up yet. It’s looking good though, the structuring and handling of overlays (step-by-step appearance of material on one slide) seems much more intuitive than in prosper. (There’s a command \pause, for instance, which introduces an overlay transition at that point.)

Both beamer and prosper are in CTAN contrib and might not be included in your distro. You can get them from CTAN, of course (links above), but beamer is also packaged for Debian, as latex-beamer. The docs don’t get put in your texmf tree though — you’ll find them under /usr/share/doc/latex-beamer.

PS: The following, which I’m going to shamelessly steal, is described (in the Guidelines) as “the central rule of typography”:

Every rule can be broken, but no rule may be ignored.