I'd like to store some files in Gmail, in order to easily attach them to letters, without the need to upload them over and over again. Maybe you know of such a service? Of course there are always file hosters.
Google Docs provides the facility to store files of any1 type by uploading them to Google Docs. From there it would be possible to email the files appending the letter text you also wanted to include into the email.
It is also possible to directly link to a file stored in Google Docs, but you might find people can't access the link due to system restrictions on which website they can access and etc.
1. I don't think this includes .exe files, unfortunately.