Yes you can. Any commercially available USB keyboard will work. I have something called the "SharkBoard". Specifically, it is meant for the Action Replay on Gamecube and for the Gameshark on the PS2. But for some reason, it works with the Wii.
But yea. Any USB keyboard will work. It saves a lot of pain for the internet channel.
Don't know the cost, but just get the cheapest you can get that can reach your wii and that works on it.
Also note, "Enter" will not work for logging into sites quickly. You have to press OK after entering your username and password. What I mean is normally on a computer, you could press Enter on your keyboard and you would be logged in without having to click "Login".
But anyway, good luck!