Depends on your budget.
For zero budget: Plenty of open source tools out there. Have to be a bit geeky to make them tick. Notepad, NVU, HTML TinyWordPress etc....
With a healthy budget: Go for Adobe's Web Premium CS4 Suite. Out of a package of 9 apps, at least 4 or 5 are web development relevant. My favorites are Fireworks, Dreamweaver, Illustrator, Flash, Photoshop...
Its easier to shell out $$$ than to learn how to use these tools efficiently and productively.