Have you tried using Google Docs?
Not for graphs - I'm currently trying Excel, but it was easy online presentation that I was looking for.
With Google Docs, you can share the spreadsheet and graph online with anyone by sending them a link to view your data.
You can set access to be read-only, or allow others to add or edit the data.
I think that approach would best suit your needs.
If you have a website, you could also publish the graph to it: https://support.google.com/docs/answer/78052?hl=en