While there may be cheaper apps that ONLY compress, I still suggest iMovie. It lets you do what you want, and while you've got it in there, hey, just throw a title and some fades on it. An extra 30 seconds of work and everyone will think you're a super techie genius.
And actually, even if you compress them, it's probably still a good idea to get Dropbox and upload them to there. Even if you compress it from 50 MB to 3 MB, I'd still rather get a Dropbox link in my email than a 3 MB file.
(Dropbox has an auto-compress setting for video. Either just use that or, if you're using iMovie first, turn off Dropbox's setting so you don't double-compress.)
