I'm with daveomak on this one: chicken breasts. Why? Because the result is very different from what you can get with any other technique. The reason? Because you cook them at a completely different temperature from what you can do with normal cooking. Dave recommended 138° F, but I go just slightly higher at 142°. Either way, this is far below the finished temperature of 160°-165° recommended with normal cooking methods. You end up with a texture and taste that is much better than conventional cooking. I love using the chicken made this way as an ingredient in something else, like a chicken salad sandwich.
I am less thrilled with doing steak this way, even though several people are recommending this. The main advantage of sous vide for a steak made from a good cut (e.g., ribeye) is really not the taste or texture, but the uniformity of doneness and the accuracy of the doneness. If you want medium rare, you will get exactly that result every single time you do it, no matter what, but if you can do that using conventional cooking you end up at pretty much the same place. Put another way, you obviously have to do the reverse sear, and once you do that, the results aren't remarkably different from conventional preparation, and you've taken hours to do what you used to do in fifteen minutes. The main reason for using sous vide for steaks is in restaurants, where they can have the steaks prepped and ready to do, and then only have to do the sear before serving.
If you want to do something with meat, look at some of Bearcarver's posts about doing extremely long cooks on less expensive, tough cuts of meat. He and others claim you can get wonderfully tender results. I haven't yet tried this, but I bet it works really well.
If you want to make recipes with raw eggs, you can pasteurize the eggs prior to using them in a recipe (like mayonnaise) and have a completely safe raw egg dish.
Here's a great site for getting more ideas for what to do with your new gadget:
Serious Eats Sous Vide Recipes