WebStorm is one from Jetbrains. Jetbrains is the company behind many great products like IntelliJ IDEA and ReSharper. They have also a complete suit of development tools for the Web which includes RubyMine, PhpStorm and WebStorm.
WebStorm provides features like:
Folder based solution management (compared to project based)
Available on major platforms including Windows, Mac OS X and Linux.
If you are considering serious Web development, I highly recommand this tool.