I'm guessing you aren't all too familiar with web dev to begin with, so if I'm wrong, I apologize.
That said, I'd recommend rapidweaver from realmacsoftware.com
Past that, I'm not sure what else makes web dev easy. You can always use things like dreamweaver from macromedia, but it costs an arm and a leg and generally is overkill for what most non pros need.
When all else fails, you should probably check out a few tutorials and fire up a plain old text editor.