Logitech Wireless Touch Keyboard K400 with Built-In Multi-Touch Touchpad - $22.99 + eligible for Free Super Saver Shipping (on orders over $25)
Sleek, low-profile keys: Easy and comfortable typing on quiet keys with bold, easy-to-read characters
Built-in multi-touch touchpad: Large (3.5-inch) touchpad with multi-touch navigation for easier web browsing
Long-range wireless: Control your TV-connected laptop from the couch with 33 feet/10 meter wireless range
Plug-and-play setup: Plug the tiny Logitech Unifying wireless receiver into your laptop and start surfing the web
For Windows-based laptops: Works with Windows 7, Windows Vista and Windows XP
Reviews - 4.3 out of 5 stars on Amazon (621 reviews)
This has been around $30-35 for a few months, dropped in price earlier today. Seems great for an HTPC.