I just came across a really simple clean javascript library, this little beauty weight in at a few KB and packs a load of effects into a very small space.
http://www.devpro.it/bytefx/it handles alpha opacity, fading, scrolling effects, expanding accordions /divs
Normally I dont recommend prebuilt javascript libraries because by the time some of them are around for a while the file size is huge and its normally quicker, easier and cleaner to make your own script to do what you want.
script.aculo.us is a primary example of a bloated library.
this one however is clean, simple, lightweight and small, plus the fact that its cross browser and in its compressed state weight in at a little over 2kb.
(or 7kb for best browser support)