You may e-mail a link instead of an audio/video file:
Problem reducing the recordings to a size suitable for emailing

You may also re-compress your audio/video files before e-mailing. In many cases it is a good idea to reduce the width and height, use the same codec when re-compressing (convert MP3 to MP3, WMV to WMV, ...). Please be more specific so that we can suggest more.