Your best bet will probably be something like a
Boxee. Bestbuy is a reseller, so you can stop by and check it out in person if you want. It appears it has wifi built-in, as well as a wired connection. It also has USB connectors for external harddrives, etc. IIRC, it will play ISO files directly, but you might want to make sure it will play those other formats you have (or convert them to something it will support).