I found authentic pad thai today at S&I Thai Cuisine in Brighton. It wasn't red and oily like Western pad thai but light-colored and not as greasy. It's the perfect combination of sweet and tangy. At $5.95 per serving (could feed 2 average eaters), it's a deal too. I also had Thai iced tea ($1.50) which was good and not watered down as well. I'll be checking out other stuff on their menu and will report as I go along. For now, I can really vouch for their pad thai. The place is small though so it's more like a take-out joint. It's great that they accept Visa/MC without a $10 minimum. They offer free delivery for those who live in Allston or Brighton.
S&I To Go Thai Cuisine
168A Brighton Ave. (at Harvard Ave.)