One think i like in KDE, the window manager that used on my Slackware system is that it already contains a lot of screen saver (if you install the package) and most of them (well, the 3D ones) are very attractive. One of my favorite is Euphoria. Look the screenshots below
Recently, i browsed to KDE-Look and browsed the Screen Saver section and i find this interesting screen saver called KCometen3. Basically it shows a comet-like effect combined with some Compiz's Cube-alike plugins (it will show your desktop as the default background, but you can change that). Since they only provide source and ubuntu package, i had to use the source and i compile it manually, but at the end, i used checkinstall rather than make install. This command will generate a tgz format which is being used by Slackware. What is the reason for this? Using tgz means It's easier to remove and it will make sure to clean up every files the package had installed. Here's the screenshot for KCometen (I have to retry several times to get the best one, but i know it's not the best one, so you might want to try it by yourself if you are interested in this screen saver).