A micro-module that allows you to keep blocks from scrolling off the screen, by using css position:fixed ONLY when needed, but move around normally the rest of the time.
Add the css class 'sticky-block' to a block to have it remain in a fixed position when scrolling. This can work for more than one element, but you'd better avoid letting them pile up.
Use something like block_class.module, or do it in your theme.
This module built as a tiny experiment, just to see if it was at all hard. Based on some code lifted from a working example on the net - it turns out to be almost trivial.
TODO - maybe add the option to anchor bottom as well. Logic is almost the same.