For large files, email isn’t ideal. That said, there are no real set rules for email attachments’ size.
I think that it is reasonable to assume 5 MB will always go through without any problem, and 10MB usually will too.
Google’s Gmail service allows upto 25 MB, though I don’t think I’d ever try sending a file of that size by email.
Blackberry handhelds can’t deal with anything larger than 8 MB, but few people read mail on their Blackberry exclusively.
Email is not particularly efficient at sending attachments though: they are 30% larger in transit than they are on your PC, so a 10 MB PDF will generate a 13 MB email
If you have a website you could use your webspace (it’s easy to upload files using cPanel or an FTP program like Filezilla). You could also use a service like Dropbox.