Blender. It was infamous for forcing people to memorize a ton of keyboard shortcuts before they could get any use out of it, but since the 2.50 redesign it has become very intuitive and its workflow allows me to work at insane speeds. Despite only being a 40 MiB download, it is a very complete tool: apart from modeling and skeletal animation, it can also do texture painting and sculpting (very similar to ZBrush).
PixPlant. There's an estimated ton of seamless texture generators out there. They all employ the same lazy technique: use a transparency gradient at the texture borders to blend over to the texture's other side. Voila, seamless. The makers of PixPlant actually tackled the problem: PixPlant allows you to select polygonal regions from a image to use as basis for a texture, applies perspective correction, tone correction and brightness correction and then puzzles these regions together so their features match up as good as possible.
Grindstone 2. Tracking time is a useful habit for a developer and having a place to write down tasks is a boon. Grindstone was a time tracker that aimed for simplicity. A task list, a play and a stop button. Things you used less often, like reporting, client/project overviews, invoices, etc. were tucked away and out of view. I'm talking in the past tense because, after a particularly silly PC World review that wanted more funny colors, they made a version 3 with a cluttered UI and pointless gimmicks like achievements (yes, really). Thus I recommend version 2, but not version 3.
Jasc Paint Shop Pro 9. It's a very fast and slim bitmap editor with tons of effects and color adjustments. It also supports layers and alpha channel editing. They were acquired by Corel which promptly added tons of bloat and DRM to it, so if GIMP and Paint.net aren't your cup of tea, I recommend the old Jasc Paint Shop Pro. It causes Windows 7 to temporarily disable the Aero shell, but works really well on Windows 8 again.
UML Sculptor. The original project hasn't received an update since 2002, but I've fixed some bugs and added .svg export to it. UML Sculptor is a UML class diagram editor that consists of a single executable. It's like drawing on a piece of paper - add a class, double-click under "attributes" or "methods," type you method name. No combo boxes, no method entry dialogs, no round-trip engineering. Ideal for brainstorming, communicating ideas and documentation.