::pats his 3Ghz iMac with a custom Penryn chip not available to other manufacturers consolingly “there there, Gigantor, they aren’t talking about you”::
Another vote for TextMate. Working with HTML you can hit ctl+opt+cmd+P and bring up a live preview window that utilizes WebKit - super super handy. When working with programming languages, TextMate interfaces with the CLI and lets you run scripts right from your text editing window (typically ctl+cmd+R). And, there’s a CodeIgniter TextMate bundle from Ben McRedmond that can seriously speed up your application building.
Coda is a nice product, don’t get me wrong, but I find it unnecessary. You can have the same integration, but much more powerful if you combine TextMate and ExpanDrive. Just connect to your remote host, drag the public_html / application folder onto your TextMate dock icon and it will create a project for you, letting you access the files as if they were local. Saving automatically updates the remote file.