I've worked in Belgium a lot over the past 10 years. I managed to get hold of a few bottles of Westvleteren 12 and it's a very nice beer, but I think there are better Belgian ales. For instance, these guys brew some amazing beers
http://www.hetanker.be/, Gouden Carolus being my favourite regular brew and their Christmas ale being possibly my favourite Belgian beer.
For barbecue I think you can go 2 ways - thirst quenching and crisp to contrast with the smoky flavours from the meat, or fuller bodied, hoppy ales to cut through some of the fat. Of the former, Shiner Bock from Texas works really well, as does something like a Duvel which is well hopped but has an almost citrus crispness. For the hoppier/heavier side I'd say American Double IPAs work well.
Another good beer with BBQ is German rauchbier (
http://www.schlenkerla.de/indexe.html), in which the malt is smoked over beech before brewing. It's like drinking a smoked bacon sarnie.