We have found that childrens' winter hats, particularly the fleece ones, make great sleeping bags for rats. Bob was particularly fond of his, and rarely slept anywhere else.
Here Jimmy takes over as the next generation of rats in hats:

I think when it comes to rat houses, bigger is better. They are smart animals, and spending day in and out in a small, unvarying box can't be to their liking. You can use solid-sided containers or cages, but I'd recommend cages for the improved ventilation. If you have to use solid sides, like an aquarium, make sure you clean the litter religiously to prevent the buildup of ammonia, which is severely irritating to their respiratory systems.
People seem to have strong feelings about bedding. Some swear by Carefresh, for example, where others hate the smell or are allergic. Some rats seem to have sensitivties as well. About the only bedding consensus is that pine and cedar are bad: the phenols can damage the lungs and possibly the liver. With Rizzo and Krycek, I just used newspaper (whole sections of paper; they shredded it themselves.) I tried Carefresh first, but they threw it out of the cage. They'd been on newspaper at the shelter, so I guess it was what they were used to. For the rest, we've used Carefresh and Cell-Sorb. I think the Carefresh, being softer, looks more comfortable that the harder pellets of Cell-Sorb, but I think the Cell-Sorb has a bit better odor control. The rats don't seem to care. Bob, since he has a bit of trouble walking, gets his cage lined with old t-shirts or receiving blankets, changed every day.
I have personally become a big fan of Martin's Cages. When we expanded the rat population last fall, we ordered a couple of R-680's (the "Rat Lodge"), one for the girls and one for the boys. They are big enough for hammocks and toys, and when the rats want to be apart (generally when there's some particularly good food around) they can go off to separate corners and avoid each other. Bob and Curly got their own 680 when they arrived.
Bob, though, started having trouble with is back legs, and he seemed to struggle a bit with the ramps. Worse, his balance started going too, and I saw him fall off the high shelf. He was fine, but it scared me...off to the pet store I went for a Super Pet cage. Super Pet cages seem to be mostly geared toward guinea pigs and rabbits (thought I've seen a multi-level ferret cage that would probably be great for adult rats; the bar spacing is too big for babies). Now Bob's on one safe level.
Curly got to move in with the girls to an upgraded cage: the Martin's Skyscraper, a full three feet high. It is the best of the cages: Curly's wheel fits on the floor, and they have a tube and a hammock in addition to the ramps and shelves.
Accessorizing the cage probably depends upon your rat. A huge favorite of our rats, especially Bob, has been a child's fleece hat with a chin strap. Oddly enough, the made-for-rat cuddle cups, which are so similar to the hat in function, have just been torn up. Some rats enjoy hiding under a plastic igloo, some turn the igloo over or ignore it. Curly is the only one who runs on the exercise wheel. (If you do get a wheel, make sure it is large enough, and avoid the ones with open wire-rats can get their legs or tails caught and injured.) The rink rats and the girls love hammocks, Bob and Curly don't. Rizzo loved the straw nest ball (especially once it got ragged and stinky. She once chewed through a garbage bag to retrieve one I'd thrown away.) Leather and Calle seem to prefer constructing their own nests out of old t-shirts and paper, much like Krycek did.
I use Critter Fresh enzyme cleaner to clean the cage pan and plastic accessories, and the cloth stuff goes in the washer and dryer. Here's a washing machine hint that it took me too long to figure out on my own: many hammocks and tunnels have removable chains for hanging. Actually removing the chains before washing saves a lot of time detangling threads from the chains when the stuff comes out of the dryer.
Whatever you do use in the cage, remember that rats live to chew. Don't put anything in the cage that's toxic or that might be dangerous as they gnaw, and don't give them anything you don't want destroyed.