We currently send emails from our applications with log files and application setting files in a .zip file in addition to the raygun report. Ideally I would have these files included with the report, so it could be opened/downloaded in the web interface. Right now we are considering uploading files to Amazon S3 and link it in the raygun report via URLs in custom data, but if you consider adding support for something similar then that would be a much better solution.
One thing that would be really cool is to view the text attacment files directly in the browser, with simple search capability and coloring of standard Log4Net and NLog output to highlight trace, debug, warning and error levels. I'm sure there are tons of other interesting scenarios for attachments and ways to view them. Images, PDFs and so on fortunately already well supported by the browser and would only need hosting and an URL.
You'll need to figure out the pricing for hosting these files and perhaps constraints on max file sizes, but I consider that trivial. Maybe include X MB of hosted storage for various plans and pay on the go if you exceed that on a monthly basis. The files would then be deleted when the corresponding raygun report is deleted.