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.
First thing I did was change the theme to the darker Specials Board which is a bit easier on the eyes and set the font to Menlo, 14pt. Also, the sidebar on the left rather than on right just feels... well, right.
The App Store version includes iCloud sync of clips and sites. However, using Panic Sync is the best way to keep things in sync across all devices.
Coda for iOS
Another on-the-go option is the iPad app Coda for iOS. 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.