Concisely display monthly archives by year with links to each month.
This is how Monthchunks looks with the Twenty Eleven theme. You can see here that 4 years of archives (eventually 48 links) take up less than 200 vertical pixels of precious sidebar real estate. Note that if you're browsing a monthly archive page, that month's number is emboldened, but not linked. If you hover over the link for any month, you'll see the localized month name and year as a tooltip.