Let me start by saying that I do not think buying a couple of cases of wine unless you have sampled it is such a great idea. Nor a great way to celebrate an anniversary - buy one bottle of exquisite vintage champagne and have a good time.
Still, if you want to go this way, here are some ideas. Do not even think about the 2006 vintage if it is about the wine. Not that there will not be good wines from 2006, just that they are not going to be easy to find yet, and it will be particularly hard to find ageworthy ones since they generally will not be released for at least another year.
If you want something that will age, and be drinkable on say your 20th anniversary, I suggest a vintage port. Buy a couple of bottles and drink one on your tenth and one on your 20th. It will be more forgiving in storage and age well. 2003 is a nice vintage and you should be able to find some very good Graham, Fonseca or Taylor at a nice price.
If you really, really want a light red, the suggestion about Bandol is good, but I think a Beuajolais Cru, say something from Julienas, Morgon or Moulin-a-Vent might fill the bill. Interesting today, would age for some years, and the 2005 vintage, currently for sale, is pretty good. This one - Duboeuf Julienas Chateau des Capitans 2005 - is available at wine.com for example and is pretty good for $16. Sam's has some interesting ones, too. But please sample them before you splurge for a case. For the most part you will find them light to intermediate in weight, with decent fruit and acid and some complexity.
A good approach might be to sample a few of those, and then buy a case or two of a 2006 when released to commemorate the marriage, though I think the 2005's are likely to be quite a bit better, on average. In fact, I think I need to go out and buy a bunch of 2005 Beaujolais Cru.
I suppose I could disagree with some of the other suggestions above, but see there is this conflict - "light red," $15 and "ageworthy" do not go together so well, so one pretty much has to compromise on at least one of these.
One other possibility is to go to
the Chicago Wine Company and buy one or more very nice older bottles, either in a normal sale or at their live auction (next one is August 29) and enjoy that. Unless you have good storage available, and even if you do, it can be a lot more fun to buy an older wine, ready to drink and enjoy it now. And you will be pleasantly surprised to find that a 1995 Bordeaux, all aged and ready to drink, can be a lot less expensive than a 2003, for instance, even though the 2003 is a lesser wine, and needs to age for a few more years. It makes no sense in a way, but it works out well. TCWC also has an interesting selection of Bordeaux in half bottles that would meet your requirements, as well as a good selection of 2006 futures.
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Feeling (south) loopy