When it comes to purchasing video editing software you might find you are faced with some nifty-looking, expensive software and some quite cheap, not so amazing looking software.
From my experience, "you get what you pay for" is not always applicable to this subject, I have found that software that is cheap like Pinnacle studio can be just as good as software like Adobe Premiere for general video editing, but if you're after top end professional live broadcast or feature film then you may as well go for the professional software like Final Cut Pro (for mac) because you might find that the all to important advanced effect you want isn't available on your cheap version.
My personal preferences are Adobe Premiere Elements, as it has similar functions to Premiere but is a lot easier to use. And Adobe After Effects which is a top end program but gets any effect you want, perfect!
Try and get software that you think suits the size and nature of your project...
Best of luck!
Roan