Where are you located? This is going to be a big factor, as quite a few sours aren't available everywhere.
Oud Beersel is pretty widely available and is one of my favorite. It's also much easier to obtain than some other Belgian lambics. It's an excellent baseline and starting point to judge other sours from.
As far as widely available stuff - try Duchesse Du Bourgogne, Rodenbach Grand Cru, the aforementioned Cuvee Renee, Petrus Oud Bruin and Petrus Aged pale. Should be a good start for ya.
I tasted the Rodenbach Grand Cru this weekend, and I would highly recommend it for a widely available sour. Chase the funk!
I would avoid Lambics until you're sure you like sours. They typically tend to be "harsher", and more expensive. 2nd to the Lindeman's Gueuze. Rodenbach Vintage Oak Aged (any Vintage) is a good Flanders Red to start with relatively inexpensively. On the off chance you can find New Belgium's La Follie on the shelves, its arguably one of the best sours brewed in America. Berliner Weissbier is also a sour style to try. Bell's Oarsman shouldn't be hard to find. Professor Fritz Briem 1809 is another good highlight of the style. Personally, I love Weissbier's and I enjoy sours, but the Berliner doesn't do it for me.
I'm a little bias because I live only 20 min from them but, I love Jolly Pumpkin. They do alot of great beers and they are all soured, thats their thing. Now I don't know your location but these are some I would recomend from them if you can get your hands on them. La Roja, La Parcela (seasonal), Biere De Mars, Luciernaga The Firefly (summer), Weizen Bam Biere, Bam Biere (saisson/farmhouse), Madrugada Obscura, Noel De Calabaza just to name a few...
I'm located in the Norther NJ, so the New Belgium is out. Thank you for the replies. My local spot has a pretty good selection, just didn't know where to begin. The above list should be a good start.
A couple more to add to the list: Liefman's Goudenband, an Oud Bruin and Cuvee de Jacobins Rouge, a Flanders Red both shouldn't be too hard to track down, and aren't too pricey. Worth every penny and then some, in any event.
Everyone already said this, but just to clarify, the Rodenbach Grand Cru and Duchesse De Bourgogne should be available at any store worth visiting in North Jersey. I'm from North Jersey also and am curious to hear what to try also. Never quite sure what to look for when I'm at the store, and am far too lazy to really look that hard.
Rodenbach Grand Cru and Petrus Aged Pale would be my first two recommendations, and then you can take it from there.
I 2nd the Jolly Pumpkin post. I have been drinking craft beer for 9 years and still don't have a taste for sours but Jolly Pumpkin by all accounts makes excellent beers and though they are incredibly small are readily available at many of the better craft beer stores in North Jersey. Also I suggest following Captain Lawrence brewing on twitter because that is the only way they advertise their special sour releases now. And start small. Go with the commercially produced "sours" and "wild ales" first and see if you even have the taste buds for real sours.
Gueuze Tilquin is fantastic as well. Blended by a man that studied under Jean van Roy (the Cantillon blender). Seems to be found at several stores around NYC including Whole Foods.
