Mac running out of hard drive space?

Last night I was trying to import some movie footage, but it said my hard drive needed like 7 GB! I have a ton of files on my computer but for some reason whenever I move the files I don't need to my trash and clear the trash, it doesn't give me any more room. How do you permanently remove files on a Mac? Or is there an online storage for files so I can move all the files there so they don't take up space on my hard drive? The files are pages, keynote, idvd, etc.