I love making seamless tiles and trying to figure out new ways to make unique ones. I was playing in PSP9 the other day and hit upon these. I really love the subtle effects of these. They're really easy to do too.
For this tutorial, you will need the following:
Paint Shop Pro. I used version 9 but if you are familiar with PSP, you should be able to convert the tutorial without problems. You can download the latest PSP version demo here.
You'll need a filter or program to make your images seamless. I've used Sandy Blair's Simple Filters - Pizza Slice Mirror to make mine. She has a great set of filters, and they are all freeware (Note: all of the tiles above were made with this filter). You can download Sandy's filters here.
Step 1.Open up a new image 100 x 100, black background.
Set your foreground color to red, #cb0f0e. Choose your paintbrush, size about 10. Draw a squiggle on your canvas.

Step 2. Go to Effects>Artistic Effects>contours, and use the settings in the screenshot.
Step 3. It's not seamless, so you'll need to make it so. Feel free to use whatever program/filter you wish on this. I've used simple filter>pizza slice mirror.
And that's it, all there is to it!
Try using different colored backgrounds and paint for all kinds of interesting effects.
For a different effect, start with a seamless background you already have and apply the contours filter using the settings above. You can also play with the settings until you hit upon something you like. Here are a couple I made that way.

Have fun with these, and I'd love to see any of your creations.