Preview.app on Mac OS X seems to work surprising well as a PDF previewer, and it is a standard part of the operating system.
I usually keep two windows open: editor and Preview.app. I use a keyboard shortcut in my editor to trigger the Latex compilation. Then I cmd-tab to change windows; when I switch to Preview.app, it automatically notices that the document has changed and reloads it quickly. It doesn't lose the current location, zoom level or anything.
Even the following kind of scenarios work flawlessly: I have foo.pdf open in Preview.app. I delete foo.pdf (e.g., using something like "make clean" or "rubber --clean" to get a fresh start). Preview.app is still happy, I can still read the latest version of the document. Then I re-create the file foo.pdf (e.g., using something like "make" or "rubber"). When I switch to Preview.app, it notices that the file has been re-created and automatically reloads it.
Regarding dvi files: do we really need those any more?-)