You can use Aquamacs, an easy-to-use, Mac-style Emacs for Mac OS X (sic.). It comes with LaTeX support built in. The only caveat is that you need to install ispell (or aspell) to get the internal spell checker to work. To this purpose you can use MacPorts or cocoAspell.
On top of Aquamacs (or of your favourite emacs) you can install the Enhanced Carbon Emacs (ECE) plugin: Enhanced Carbon Emacs is now a universal enhancement plugin for arbitrary (unix, carbon, or aqua) emacs distributions (such as Yaced, Aquamacs, CarbonEmacs Tiger, or the native darwin emacs in /usr/bin/emacs). This includes a fully customisable LaTeX editing environment based on AucTeX, RefTeX, Preview and other packages. Basically, ECE is a convenient way to properly install a large number of pre-configured useful packages for LaTeX users, which includes a hack of AUCTeX, that allows to have a more intuitive handling of the “view” command in a macintosh context (in particular, for non-pdftex users willing to preview in pdf).
There are other alternatives, like iTeXMac or TeXShop.
Apple Preview.app doesn't reload the PDF file when it changes, which is kind of annoying. A good PDF previewer for latex is PDFView. You can use TeXniscope which works with DVIs as well; but it doesn't seem to play well with intel macs.
Check out LaTeXiT, handy in combination with Keynote, Powerpoint, or other software in which you want to include latex snippets.
As for bib files, BibDesk is a graphical BibTeX-bibliography manager for Mac OS X; it also allows you to export to HTML and RSS.