I've been using one a couple of days a week for the last 7 months.
So far I have used it for:
Chicken breasts
Chicken thighs (boneless and skinless)
Steaks (ribeye, strip, filet, sirloin, flat iron)
Salmon
Shrimp
Scallops
Baby Back ribs
Pork chops
Eggs (poached, and hard boiled)
Asparagus
If you don't already have a cast iron skillet and a decent torch (Bernzomatic TS4000 from the plumbing tools aisle at Home Depot) then you're going to find yourself far behind the power curve.
The secret to chicken is the final sear. Chicken held at 140 degrees for 35 minutes is perfectly safe to eat, and incredibly juicy, but without searing you will likely find the color and texture to be unappetizing. Boneless/skinless breasts are nearly impossible to work with here--the outer layer will become stringy when high heat is applied. The best way to do them is to cook them in a sugar heavy marinade (commercial bbq sauce is fine for this, as you want the sugar for caramelizing at the end), and blast with a torch just before serving. A traditional skin-on breast is ideal, as the skin can take a solid sear in your cast iron.
Steaks prepared sous vide are absolutely fucking awesome. I've been using nothing more than sea salt and fresh cracked black pepper, and cooking at 132 degrees, followed by a very brief (30 seconds, roughly) sear in an abusively hot cast iron skillet. The top sirloin filets I've been getting from the meat market can be cut with a butter knife when they're done. The impossibility of overcooking has led me to a renewed interest in sauces, culminating in me recently mastering bordelaise sauce. I find it to be the ideal topper for a steak--as a bonus, it tastes so good, that I can cook filets now for company and not be bummed out about having to eat that flavorless, overpriced cut. The lack of temperature gradient inside of the steaks is a big selling point of the method.
Salmon has worked well for me, with and without a final sear, usually cooked at 122 degrees. I've seen several people mention the need to brine salmon before cooking in order to prevent the albumen build up on the surface, but I have never had an issue with that, and I suspect that it will only become an issue at higher temperatures (every recipe that I see call for brining also uses temperatures above the 122 that I use).
Shrimp was an interesting experience. I cooked it with lime and jalapeno (the shrimp were destined for shrimp tacos with a mango salsa), but I don't remember the temperature that I used. The odd texture of the shrimp is the reason I bought an over powered torch for finishing foods--having the shrimp be the exact same texture throughout was confusing, and I realized that I needed that slightly overcooked layer on the surface in order to give them a little snap.
Scallops came out well, but I decided that preparing them sous vide is unnecessary unless you have really, really thick ones. The average size scallops that I get from the grocery store can be easily cooked to perfection in a hot skillet in a minute or two. The only time I would consider doing them sous vide now is if I have someone who doesn't care for the texture--I can get them good and firm in the water bath, without overcooking the outside.
Baby Back ribs I just made for the first time for my dad for Father's Day. Personally, I feel that I under seasoned them, but that's easy enough to remedy. I ran this batch overnight at 145 degrees (short notice, I've been meaning to do a 24-48 hour 138 degree cook), and found them to be extremely tender and juicy. Next time I'm going to put some sauce on them when they go into the bag and see how much of that flavor gets cooked in. A quick finish on a hot grill or a minute with a torch to caramelize the sauce and you're good to go.
Pork chops I usually do at 140, and sear in browned butter as Kenji recommends on SeriousEats. The only issue I have run into with the chops is, much like the baby backs the other day, that you will wind up needing more seasoning than you think. A quick honey/teriyaki/bourbon reduction in a sauce pan saved my ass on those. You won't believe how juicy they can be.
Eggs, I just follow the SeriousEats guide as far as time and temperature. Hard boiled eggs come out well, but poaching eggs is where the machine really shines. You can poach an egg in the shell (45 minutes at 143 degrees, if I recall correctly). For planning purposes, Poached eggs can be stored in a bowl of water in the fridge for a couple of days, and warmed up in a bowl of warm water a few minutes before serving. Serving eggs benedict to a crowd for breakfast? Easy. No swirling the water around, no gently cooking the eggs one at a time, no starting over when you break one. Cook them up, in the shell, the night before. Reheat on demand and drop them on the muffin. On an unrelated to sous vide note: go buy an immersion blender. You can make hollandaise in a couple of minutes, without the hassle of constantly whisking it in a double boiler.
Asparagus is pretty good when prepared sous vide, but like scallops it isn't really necessary. I find that I really miss the little browned bits that I get from higher temperature cooking. If you decide to try it, I recommend starting with
this recipe. The sauce in that recipe is very good, and I feel that it works even better over some asparagus that has been sauteed at very high heat.
On an equipment related note: Make sure that you get a vacuum sealer with a 'moist' setting. I went cheap on mine, and it really limited my ability to cook with marinades, because the liquid would sometimes prevent the foodsaver from getting a good seal on the bag.