Depending on the host's place in life at the time of the home purchase, sometimes just the most basic things can come in handy.
If it is a single person with their first home, or a young couple starting out that is financially strapped from either being very young and never having lived on their own, or paying lots of student loans etc. a very nice laundry basket filled with cleaning and household supplies might be well received.
Things that really add to the grocery bill, but everyone needs, like paper towels, tissues, bath tissue, liquid hand soap, dish soap and/or for the dishwasher, foil, plastic wrap, zip lock bags, cleansers and cleaners for the bathroom, a nice toilet brush set, window cleaner, some laundry soap and softener, nice microfiber towels, Supercloths, or Bio Cleaner cloths, and anything else you could think of to clean house.
Or do a linen version of this. Fill it with dish towels and cloths, a nice bath towel set and maybe some cream or white sheets for the bed (if you know their size). If you have a favorite linen spray, that would be nice in there too.
Or a garden version with some gardening tools in a caddy made for gardening, and then add a good shovel, rake, broom etc. especially if they are coming out of apartment life and have never taken care of a yard before.
The problem with housewarming gifts is that it depends on where people are at in their lives, what they already have or how very much they still lack when setting up that home (and that often has to do with their age, as if they are getting out on their own for the first time, it would be very different than people in their late 50's downsizing into a smaller place), so be sure to consider that factor when trying to choose something.