The best way to do this is with an HTML table. The tab key doesn't work on the web, and using spaces typically doesn't either since the wordpress software strips out multiple spaces. And, given that browsers all render slightly differently, what looks acceptable in one browser will not in another.
See #7 here in this post by Panos: http://wpbtips.wordpress.com/2012/02/05/introduction-to-html-for-wordpress-com-users/3/ .
There are also many online HTML table generators you can use, but they all require a little cleanup since most of them have not yet adjusted for HTML5 and include some depreciated and obsolete code that will have to be edited and replaced.
You can also create the table in Excel or another spreadsheet program and then export that table as HTML. You then open that HTML document in a plain text editor and copy out all the code for the table itself and then paste that into the HTML tab on your post or page.
<table>All the code for the table</table>
Again there could be a little clean up required.