Languages

You have several options for languages:

HTML
Chances are you're going to be using this. I don't need to explain.
XHTML
This is a new version of HTML. If you saw it, you'd say it's HTML. The only real difference is that it follows the premise of XML: Every tag that's opened must be closed. That includes paragraph tags and even image tags. XHTML also forces the use of CSS for formatting. Font tags are illegal here. This site is written in XHTML.
CSS (Cascading Style Sheets)
I would encourage everyone to use CSS as much as possible in their pages. It standardizes formatting and eliminates the need for any font tags. It can also get you some formatting that just isn't possible with HTML. Using the same style sheet across several pages will also reduce bandwidth usage as the browser will only have to download style information once. To experience the power of CSS, see CSS Zen Garden.
JavaScript
Some necessary effects can be achieved with JavaScript, like replacing text at the click of a button without refreshing the page. But be careful not to overuse this. There are many code snippets out there that let you do cool things, but really are useless or even annoying. As well, many functions commonly implemented with JavaScript, like menus and rollover effects, can often be better implemented using CSS.

A good place to learn any of these languages, or many more, is W3Schools. There are definitely other languages you can use, but these are the most basic.

Editors

The editor you use is also important. Most beginners will use a WYSIWYG (What You See Is What You Get) editor like these:

Dreamweaver
From Macromedia (now Adobe), the same company that brings us Flash, comes this devolopment tool. They make a very good effort to support as many languages and features as possible. Definitely recommended if you want a WYSIWYG editor.
FrontPage
This editor from Microsoft has been around forever and thus is the most popular. It is also the most frustrating to use. However, for simple sites, it does the job.
Nvu
This editor is the stand-alone version of the editor included in the Mozilla suite. It's open source and runs on Windows, Mac, and Linux.

Nvu, the complete web authoring system

Be warned that these editors create horrible code (such as tables within tables within tables). Also, if you add code yourself, they have the tendency to change your code to their style when you edit your page in visual mode. This may change the look of the page from what you wanted, and can be very annoying.

If you are comfortable writing all the code yourself, I would encourage it. It may take time to become comfortable with it, but you will have the most control over your code. However, there are better alternatives than Notepad. Here are a few code-only editors:

CuteHTML
This is a great editor from GlobalSCAPE (of CuteFTP fame). One of the best features is that it tells you which tags or properties are supported in which browsers. There is a regular version, and a Pro version with extended features. Both versions have free trials, but require you to pay if you continue to use it. If you are going to pay, I would definitely suggest investing in the Pro version.
PSPad
This is a free editor. I used it for a while myself. It is only available for Windows, but has many features to make coding easier.
Vim
This is what I use now. Vim is an open source editor designed and mainly used under Linux, but Windows and Mac versions are available as well. It comes in two flavours: the most often used command line program, and the windowed version. It includes very useful commands to speed up the editing of code and is designed so you never have to reach for the mouse. There is a bit of a learning curve when beginning to use it, but it comes with a tutorial to help you, and it's certainly worth the time. I personally think it's impossible to learn everything there is to learn about Vim.

gVim, the windowed version of Vim
XEmacs
Built from the Linux editor Emacs, this editor has much the same goal of Vim, to speed up editing. It can do the same things but with different commands. If you ask around, you will find there is quite the war between Vim and Emacs loyalists. If you're interested, you'll have to just try each and see which you like better.

All of the above editors are customizable, and include very useful code highlighting for easier reading. Dreamweaver, FrontPage and CuteHTML have code completion as well.

Image editing

Most websites need pictures. To make pictures you need an image editor. I probably don't need to say this, but get something better than Paint. The best editors out there are:

Adobe Photoshop
The leader in image editing, and by far the most popular. However, it comes with a big price tag.
Paint.NET
An open source image editor that aims to be a Photoshop replacement.
GIMP
An open source image editor with many of the same features as Photoshop. If you like the feel of Photoshop better, you can try out GIMPshop.

The programs I've mentioned here are just a sample of what's out there. Do your research and try a few out to see what you like before settling on one. Whatever you use, learn it well. Every language and program has its own features and strengths. Know what they are so you can take advantage of them. There are plenty of tutorials out there on everything.