Thord Daniel Hedengren has written a series of posts that argue blog sidebars are being rendered useless by widget clutter.
He takes a look at things bloggers should and should not be doing with this valuable but often "wasted" inventory.
Here are Thord's tips...
Remove ‘widget clutter’
As Thord points out, some widgets can be useful for blog readers, but many are unnecessary, add nothing to the user experience and can lead to slow page loading times.
Information about the blog author is useful to reinforce the trust of readers, and helps them understand where the writer is coming from. A short description with a link to further information may work best.
Add a recent comments/articles list
This is something that adds value for the reader, allowing them to quickly see which articles are provoking most debate. This is also a useful way of promoting other content.
The sidebar is the best place for adding RSS feed options, as well as newsletter / email sign ups.
If you use a service like Twitter, then add this content to the sidebar, so readers will get used to looking for it there.
Categories / tags
Long lists of categories and tags can be ugly to look at. Although they can help readers find content, it’s best to limit the number of categories on display.