I always just assumed that slide transition animations are limited to WYSIWYG presentation programs. Turns out you can define slide transitions in beamer by default without any special packages.
See Chapter 14.3 of the beamer documentation for all the available transitions and their options.
Some of the transitions seem to be wonky though, with some parts of the slide being hidden or cut off after the transition.
Disclaimer: This is something I just learned so I might be completely wrong. If I am please let me know, my email is in the footer.