Sorry to say this, but that is an incredible ambiguous question. What do you want the plug-ins to do? There are no "make it look cool" plug-ins as they all have specific tasks. For example, Trapcode have a range of awesome plugins, but they won't help you much with colour correction.
It depends a lot on what you want to achieve, and what it's worth to you. Is there any more info you can give us - there's seriously hundreds of plugins and a lot of them have a specific function so it's difficult to say "here, buy this one".
Alex
Lightdrop Video Production, Editing & Design
