This morning I found Quicksand, a jQuery plugin for easy filtering of elements using really nice animations. Have a look, try it and say that it’s perfect for an archive page like the one tumblr uses. Sadly, you can’t change the template of the archive page on tumblr. (If I’m mistaken with this, please contact me!)
Well, let me tell you what archive page I would like to create (and maybe will create for another site in future): On top you have this tumblr-like selection of year, month and, as I would really like it, a tag cloud for a general filtering by subject/category. And, a search bar. Actually, I would like the search bar to be on the left, followed by the tag cloud in the middle and then the years and months. This area would have a fixed width so that you have to scroll vertically to reach the earliest years/months. And of course, you could combine these filters. Beneath that, I would like to see the articles put in little boxes similar to how they look on tumblr right now.
This is where Quicksand comes in. When you apply filters the new set of article boxes is instantly loaded via AJAX and replaces the currently visible ones using the effect Quicksand comes with. IMHO, this would be a pretty cool archive browsing experience!