Since my Shintaro wireless keyboard decided to go on the fritz, I needed a cheap replacement while the Shintaro goes off on its warranty journey.
The Rapoo RP-X1800 was $19, and I have to say I'm pretty impressed with it. They keys are a little squishy (as to be expected with a cheap keyboard), there is no caps lock LED (also common for wireless keyboards) and no off switch on the keyboard (there is one on the mouse).
But the wireless connectivity was flawless. Compared to the Shintaro, which was never quite right, the Rapoo just worked straight away with no key presses lost, and moving the mouse will wake the computer from screen saver, something the Shintaro trackball never did, to my annoyance. The wireless USB adapter isn't as small as a Logitech one, but is smaller than Shintaro's.
The biggest drawback for use as a HTPC input device is the separate mouse and keyboard parts, but I'd have no hesitation recommending the Rapoo X1800 as a solid budget wireless KB/mouse combo.
After running with this combo for a while now, I have noticed occasional glitches when typing, usually trying to type something really fast. Isn't much of an issue (doing passwords is probably the most annoying), but I didn't notice this issue when I first started using the Rapoo so thought I'd update to mention it.
For me Logitech is still the best as far as quality of wireless connectivity goes.