This procedure gives some very nice looking sidebar backgrounds with a minimum of effort.  Start out by opening a new file, about 300 x 300 pixels, with a white background and 16 million colors.  Now play around a bit with your filters. There are several nice pattern generating filters available, either in the Filter Factory Galleries, or in Krusty's Filter collection. Here I've used one of Krusty's filters called "The House that Jack Rented", followed by some distortions. If you don't want to create your own pattern, find a texture that you like, and with the Flood Fill tool set to Pattern, fill the new file with the texture.
 
 

Now choose a part of your new pattern that you like. Using the Shape Select tool, outline a rectangle about 50 pixels high by 120 pixels wide.  Smaller or larger is fine, depending on the effect you want. Go to the Edit menu, and copy the selected area to the clipboard.  Now open a new file, 200 x 200 pixels, with a white backgrond and 16 million colors. Go to the Edit menu again, and Paste as a new selection.  Position the rectangle near the bottom of picture.
 
 

Next, paste the selected area into your new file again. With the area still selected, go to the and choose Mirror. Then return to the Image menu, Rotate : 180 degrees. Position the rectangle right above the first one, so that the two patterns match. You now have a pattern that will be seamless when layed top to bottom.
 
 

Now, using the Shape Select tool again, draw a rectangle completely around your pattern, and copy it to the clipboard. Next, change your background color to white. In the Edit menu choose Paste: as a Transparent Selection. This will put a second copy of your pattern in the file. Now go to Edit:Copy. Finally, Paste: As a New Selection.
 
 

To turn your pattern into a sidebar, Go to the Image Menu: Enlarge Canvas. Take note of the height of your pattern, and fill that into the Height Box. Make the width 1000 pixels. This will ensure that your sidebar will be wide enough no matter what resolution your viewers have their monitors set at.
 
 

Now you can add a bit of color if you want. Use the Area Select Tool (Magic Wand) to select the long white area. With the Flood Fill Tool, Color this area with a shade complimentary to your pattern. Of course, you can also leave the area white if you wish.  Here I've used a very light shade of blue that appears in my sidebar. Be sure to leave the area selected for the next step.
 
 
 

Now we add the final touch. Go to the Selections Menu, Invert. The highlighted area should now be your pattern. Go to Images, Special Effects: Drop Shadow. Set the shadow color to Black, the Opacity to 255, the Blur to 36, The Vertical Offset to 0, and the Horizontal Offset to 5. The shadow sets your sidebar off from the text area beautifully.