I am not sure if these outlets can be shared to everyone easily, but attaching the document to a google docs or dropbox, etc. site may allow you to just post a link where people can click on it to find the document. It is essentially a document sharing website.
It is true you can't attach Excel documents in posts on this board.
However, if you have an Excel spreadsheet you want to include in a post, you have a couple of options.
The site supports BB code, which includes support for tables. In theory, you could save your Excel spreadsheet as an html document, then copy and paste that html code, which should essentially be a table, into your post and voila, the data would be there, nicely formatted.
Unfortunately, you have to do some work to get the format changed to bb code standards. First thing is to replace all instances of < with [, then all instances of > with ]. BB code doesn't understand sizing, column spanning, and some other stuff you get when you turn an Excel spreadsheet into an html page, so you will have to remove that (I just used replace with nothing) or figure out what the BB code syntax is and use that.
The table below is what I got playing around for 5 minutes. It isn't pretty but it could be with a few more minutes of tweaking.
I think the easier path is to save your spreadsheet as a pdf file and attach that. The newest version of Excel has a save as option that allows you to do this directly. This is what I do with the NYS football prospect posts I make,
If you are working with an older version, you can use one of the free pdf conversion programs or if the data all fits on the screen at the same time, copy your Excel window into MS Paint and save it as a png, jpg or gif.