You have a couple of options here, depending on what you're comfortable with and your price range. At the very top is the
Logitech T650 wireless trackpad. It is expensive, around the same price as the Apple Touchpad, but is very high quality with a glass top. The prices for the T650 are through the roof on Amazon, so if you want one at MSRP, you'll have to buy from Ebay if you are comfortable with that. The
Dell TP713 is another option, While it isn't as good as the Logitech pad, it is still a solid unit and is priced a little cheaper. If you don't mind a cable, the
Sedna Touchpad is a decent unit with some nice features like programmable hot keys. It's a great touchpad for the price.
Alternatively, if you already have an Apple Magic Touchpad, or like the product, you can connect your Apple Touchpad to any Windows machine. If you try connecting it via Bluetooth and get no results, you'll have to download some drivers to get it operational. Hope this helped, take care.