If by commercially available you mean the supermarket, then Franziskaner, or maybe Warsteiner. Depending on your area they should be fairly easy to find. Franziskaner is a hefeweizen with banana and clove notes, no carbonation, lots of head. Fairly thick, but definitely a light beer, great for summer. Warsteiner is a bit malty for my taste, but it's cheap and a good session beer.
If you're willing to look around a bit, there are a ton of great beers out there. I prefer hefeweizens, pilsners, or some ales during the warmer months. Schneider makes some fantastics hefes that are really starting to gain traction in the northeast, depending on your area you should be able to find them or at least have them ordered at your more discriminating stores. Their regular Weiz and Weiz Hell are good, but their Aventinus, a doppelbock, is one of my staples. And if you really want to treat yourself, pick up a six pack of their Eisbock (it'll run you a good 50-60 though.)