After having about all the cases I could take at CES, I stumbled upon the iLid booth with a weary eye. I vaguely remembered a Kickstarter campaign a while back, and the case -- which is also a wallet -- was for the 4- and 4S-sized iPhone. It seemed like a cute idea, but these things are often better in theory than in practice. However, at CES I got a sample of the iPhone 5 version and since then I've been trying it out. It's great, especially if you like to keep a small wallet or have less stuff in your pockets.
iLid is a plastic case which puts a small chamber on the back of the iPhone. This chamber snaps tight, sealing a couple of cards, a small (flat) key and possibly a couple of bills inside. I typically carry just an ID and my bank card, so the possibility of a couple of bucks floating around isn't that big a deal to me. There's a clip on the inside lid to secure bills, but I put my bank card there. My ID clips neatly into the other side.
Yes, the iLid makes your iPhone thicker. I found that wasn't a big deal. I do love the thinness of the iPhone 5, but having all my stuff in one place is worth the bulk. The iLid plastic is very durable, and it has resisted scuffing and scratches. It's also very light, so "bulk" in this case is more about added size, which I'm not minding either as the iPhone feels a bit more like the phones I grew up with -- bulkier things that were pretty comfortable to hold in one hand.
If you want a wallet and a case, the iLid is pretty great. It's also less than US$40, which is a good deal for a case to begin with. I feel like the iPhone 5, with its sleek profile and greater length, makes the iLid case really worth it.