After playing around in photoshop, I stumbled across an extremely easy way to make simple, repeatable patterns. This tutorial will translate into any program, but was made in Photoshop 6.
I started with a 100px by 100px canvas because I was going to make a simple checkerboard brush for my icons. Here is one of the brushes that I ended up making.
Making a brush like this is really simple. I just used the 5px square brush that is a default in photoshop. If your program doesn't have a default square brush, just make one by creating a 5px by 5px (or whatever size square you want) canvas and fill it with black. Then turn it into a brush (Edit -> Define Brush in photoshop).
I made two other brushes that look like this:
and
Define the new brushes you created, so you can apply them in any color.
I decided to see what would happen if you overlapped them, and was pleasantly surprised to find that it created a pattern. So using the three brushes in different colors, this is what I got:
in
in
in
all to create this:
Here are the variations using just two of the brushes:
By varying square size and pattern, you can create all sorts of pixel patterns very easily.