First of all, what are you going to put in the sidebar? Is it going to be for navigation? Are you going to use it for extra, less important things, like widgets and blogrolls?

I’ve found that navigational sidebars are more effective when placed on the left, rather than the right. Meanwhile, sidebars with less important things should go to the right, as you want people to focus on the content more. I find a left-hand navigational sidebar more comfortable than one on the right, don’t you? Maybe it’s the whole reading-from-left-to-right thing.

So, remember this:

• Sidebars that are mainly navigation should go on the left because it feels more natural to look for navigation there. If you have a lot of navigational links, it might be a good idea to put them in a sidebar.
• Sidebars that are mainly less important things should go on the right, which distracts from the content column less. If you don’t have many navigational links, and you can put them in a horizontal navigation bar near the top, you’ll probably want to go with this option.