I've never seen an amazing order confirmation / invoice email. Even the best html5 websites send terrible order confirmation emails (sometimes in plain text). I believe this is because invoice's usually require the use of tables to show the purchased items, which is extremely hard to implement on a mobile devices.
I found some tricks to making tables more manageable on mobiles: http://css-tricks.com/examples/ResponsiveTables/responsive.php, but for an order confirmation email, this approach wouldn't be practical for an invoice table.
Are there any alternatives to making an order confirmation email look good on a mobile devices? and when making an order confirmation email, should you stay away from tables?
You can use liquid layout so set all width and to be in percentage. I would also look into grid layouts or column layouts.
So far most big sites like eBay Google and so on still use tables to send out their emails. Tables are are still useful and used widely but with the new css3 like flex, column-count, grids .. tables will probably deprecate in the future.
Again the new CSS3 features are still in testing so not compatible on all browsers.
http://www.w3schools.com/css/css3_multiple_columns.asp
http://www.w3schools.com/cssref/css3_pr_box-flex.asp
How about something like this? This uses a fluid/liquid technique that works on all major clients, including those that do not support media queries (Gmail etc...):
Just be aware that this template doesn't act fluid when resizing your browser window. It works in all major email clients however.