Raisr made a nice job of putting tabbed widgets in the ChannelPro theme.
I use tabbed panels for post navigation, but it's just controls dropped into each panel.
That's an easy way of doing it if you just want to get something working for your own site.
Also, it makes it pretty easy to open the tabs at the right place, if browsing by date for example, then the date tab is active with selected year and month in view.
Have a look if you want
There are accessibility issues with tabs, which I've just about got ironed out.
Having said that, I'm considering simple links in the sidebar(taking up hardly any space) that take you to tag, category, date and author pages.