Here are some plans to build a brick bbq grill courtesy of the Brick Industry Association web site.
It's a simple design for a basic grill, but I think they could be adapted to various other applications, such as adding a fire box and door for low and slow cooking.
Here's an article from CBS News about building a "classic brick barbecue" and another article from DoItYourSelf.com about building a brick barbecue.
Finally for those that don't mind spending a little money, here's a link to bbq smoker plans. I haven't purchased the plans myself, but the description from the Code-Electrical.com web site says they are "complete step-by-step plans for the do it yourselfer" with pictures.