Here's the "famous" Texas Monthly "Top 50" article on TX BBQ: http://www.texasmonthly.com/magazine/bbq
They named Snow's as #1. As a result, I have seen Snow's featured on (and getting the highest praise from) all over the "foodie" cable networks. Problem is that Snow's is only open Saturday mornings, so your friend had better be a hardy purist to tackle Snow's.
If your friend is a "semi-purist" BB's
recommendations above are excellent and more easily visited.
If he just wants to "chow down" at a place which has been featured and highly praised on all the cable shows - Bourdain, Richman, Flay, etc. have them go to the Salt Lick: http://www.saltlickbbq.com/
. This is "showtime" open pit BBQ with all the "niceties", i.e., knives, forks, plates, sauces, etc.
Wherever they go, they are in for a real "Texas Treat".