It's the week of the slideshows at Google. After the Gmail slideshow for presentations, Picasa Web lets you create a sleek slideshow for each one of your albums and embed it in your blog. It's not as hot as Monoslideshow, but it doesn't cost $20 either.
The options is available only for your albums (both public and unlisted), but if you change the albums ID and the username in the code you could use it for any album from Picasa Web.
If you want a customizable slideshow and you know some JavaScript, there's an AJAX slideshow control launched by Google as part of their API for feeds. You can use it for any MediaRSS photo feed (like the feeds from Flickr), change the number of images, the scaling, the transition time and other options.
A similar AJAX slideshow available only for Picasa Web Albums, but easy to create even without knowing JavaScript, can be found at this site.
Related:
Google's photo screensaver