I prefer to place the final art in a zip file on my ftp server, then send my customer the url of the zip file (loading the link starts the download in most web browsers).

I can also send the final art as an email attachment, or through an alternate file delivery service if requested.

I send black & white line art cartoons as greyscale 600 dpi pc or Mac tif files.

Color art can be sent as either RGB or CMYK 600 dpi pc or Mac tif files.

I can also deliver the art in jpeg, eps (raster art, not vector art), or other file format if you prefer.

I work on a Mac running OS 10.4.9, using Photoshop CS.