This one is an assassin bug. It’s actually in the same family (Reduviidae) as the Thread-Legged Bug from last week, but it certainly doesn’t look like it:
Specifically, I think it is Reduvius personatus, commonly known as the “Masked Hunter”.
When I found it crawling on the bedroom window, it didn’t move very fast, and didn’t look like an aggressive predator, so originally I thought it was one of the plant-sap-sucking bugs. Specifically, I thought it might be a Squash Bug, which looks similar but not identical. I understand that the most visible difference is that the assassin bugs have a distinct “neck” while the squash bugs do not.
The antennae are very long, I had to take a special photograph to fit them in. There are actually only a few segments in the antennae (it looks to me like there are only 4, as compared to what look like sometimes over a dozen for other insects), so they aren’t particularly flexible.
Like all true bugs, they have piercing/sucking mouthparts, so instead of chewing up their prey they have to suck out their juices. They may inject digestive fluids into their prey to liquefy their innards first, like spiders do, but I don’t know for sure.
Reduvius personatus is commonly found in houses, like this one was. The adults are pretty easy to spot, but the nymphs often aren’t – they have sticky bodies when they are young, and collect lint and other debris until they look like little dust balls. So, if a “dust bunny” under your furniture moves under its own power, it might be a live one, and could bite. Mostly they don’t bite people, though — they prey on other small insects that they find around the house. Interestingly, they are reported to be pretty effective predators of bedbugs, so they might actually keep you from being bitten.
 As a result, I confess that I didn’t handle it very carefully. It didn’t bite me, though. Just lucky, I guess. Incidentally, S_ says that one of these days, I’m going to have to write something like “The bite of these insects is, as advertised, extremely painful”, or, even worse, “I must apologize to my wife for telling her that this one was probably harmless . . .”
 On further checking, I see that yes, Assassin Bugs do use external digestion. This would certainly account for their reputation for having excruciatingly painful bites. I think arthropods are ideally suited for being eaten this way. The exoskeleton makes a nice, solid, relatively inert shell to hold the injected digestive fluids in while the innards are liquefied, and then the predator can just suck it all up and throw away the chitinous husk. Convenient.