HTML and CSS
Perhaps the most powerful tools in this category are the Adobe Dreamweaver (Mac and PC), Microsoft Expression Web (Windows only), and Kompozer (free, open source; Mac, Windows, and Linux) type programs. These software programs include powerful features that even have some WSYWIG-like functionality, though not nearly to the same degree as products in the other two categories. Their foundation is grounded in HTML and CSS code, but have some advanced quick previewing tools that allow you to quickly see how changes in the code affect the site.
For some, these programs are a great tool. For others, the complications put too many constraints on their work. Those are the developers who prefer to dig into code their own way. There are many advanced text editors that have been designed specifically to help make coding easier with features like smart coloring and powerful find and replace.
BBEdit and its free counterpart, TextWrangler, are well-known HTML editors for the Mac. Their advanced features make seeing the code easier and help when organizing multiple files. Coda, another Mac-based piece of software, combines several tools into one easy application: text editing, advanced coding tools, CSS editing, file management, and live previewing. NotePad++ and Komodo are Windows-based advanced text editors.