Granted, it doesn't have the full-on extensions capabilities Firefox users get addicted to, but there's still plenty you can customise in Internet Explorer 8 even without playing with the new Web Slices and Accelerators features.
The IEBlog runs down the options built into IE8 for customising the menus, favourites and toolbar areas, ranging from changing the size of each displayed favorite to switching off the favorites bar altogether (the option I choose as a dedicated minimalist).
One potentially useful idea if you're working on a large screen: move the toolbar to the top of the screen so you can fit more tabs across the main page. (One tip: As well as unlocking the toolbars, you may need to widen the toolbar before you can successfully drag it to the new position.)
Customization in IE8 [IEBlog]