On Windows, the newer Windows Live Movie Maker works pretty well compared to the old Windows Movie Maker (and can handle HD), but it is still pretty limited compared to the non-free options.
A good value option for more capability is Adobe Premiere Elements, which you can get for about $80. I think Sony Vegas Movie Studio is another lower-cost alternative with a lot of capability, but I haven't used it. Of course, if you have the money and high demands, go for Sony Vegas Pro, or Adobe Premiere Pro.
For a Mac, if iMovie doesn't suit your needs, the Adobe Premiere options are available there, or you could get Final Cut Pro.
Last edited by herzogone; 11-11-2011 at 03:52 PM.
Reason: Mac info