Choosing a development environment can be a challenge, but I’ve been happy with Coda from Panic Software. Coda offers most every tool I need in a single application. Targeted to web development, Coda offers syntax highlighting for over twenty languages & formats, searchable online manuals, and live preview using Safari’s WebKit. Sometimes the simplest things are nice, and the Sites pane with a thumbnail view of each site makes managing and finding dozens of sites a snap at work. Even though my office is a Microsoft shop, I use Coda as my primary coding system.
I keep finding new uses for Coda, too. Yesterday I was saved by the token-based find-and-replace, which let me perform complex actions without the effort of building regular expressions. I’ve used the Subversion support for pulling source code or projects in which I am interested; I’ve used the Publish function to unify local and remote directories over FTP without worrying about skipping or replacing files.
Coda isn’t free, but I depend on it every day, and gladly recommend it. They’re at version 1.6.3 and it just keeps getting better.