Making files smaller without losing quality?

Me and some friends are doing video recording/editing and need to send the files to each other. However the site limits how many GB's you can store so we need to find some way for people who are recording to make the file (video&audio) smaller to send to the editors without compromising quality.

One person mentioned that .flv makes the file smaller but I don't know if this is lossless or not. I've also heard 'codecs' tossed around a lot and understand they're used for what we need but don't know which one would be best or how to find them.

So question is, what is the best way to make video&audio files smaller so they can easily be sent&received for editing?