Coda is by far the absolute best web development tool available on any operating system... and I've tried many. It is customizable, supports the latest version control and server connection methods and is lightweight though feature rich. Since I work on many projects, its project-centric code management features helps me remember what I've done and what's ready to go live.
The latest version, Coda 2, is great. Has a streamlined UI that really speeds up development time. With books, code complete and a MySQL editor it's a complete package for web developers who do their work on a Mac.
Not a huge fan of the default editor font. First thing I did was change the color to a light-on-dark scheme in the editor and switch from the Menlo to Monaco font. Might like Menlo better on a retina display, but until then I'll stick with my pixel-precise fonts.
I got the App Store version which includes iCloud sync of clips and sites. Very handy in keeping my setup consistent between notebook and desktop. Things get a bit more complex when dealing with SVN repositories and such, but when I'm on the go it's nice to have things pre-set up for me.
Another on-the-go option is the iPad app Diet Coda. Though it doesn't do everything Coda does making it an alternative to the full app itself, it's a handy tool for quick on-the-go edits to my sites via FTP/SFTP/etc.