Depends on what your definition of special effects are really. There's lots of tools out there but without knowing what you want to do it's hard to tell you the shortest route to take. For instance are you looking for something to add titles, edit timing, or composite 3D animation into the footage?
I'm usually using VideoSkin. it's looks like girl's toy but with correct attetion becomes very simple and powerfull tool (if you know flash enought to make your own bunch of skins-filters for one) also very good it's working realtime so can be used to add ur effects before stream will be used whitch is usefull too.
ps main advantage to me that it's free app with very simple interface.