Once you have your box thats ready to throw out all that great content, you will then need a way to control the box. You can use a usb mouse and keyboard but that could look naff with wires all over the place, and it doesnt go with the home cinema look. There are a number of ways to control your HTPC.
To control your home theater needs a mouse and keyboard (after all it is a PC). But there are many wireless devices such as an a wireless mouse and keyboard, and wireless media center remote controls. You can find these easily on Amazon and eBay from around $20 and upwards.
Also available are trackballs and Universal Wireless PC-TV Remote Controls that will work across PC's and oother streaming devices. The other popular option is to use your mobile phone as a remote. Both android and iOS devices have literally hundreds of apps that can control xbmc and devices using the smartphone and tablets touchscreen ias a remote. The app needs installing on both yourmobile device and PC.
There are many wireless keyboards available that connect to your HTPC by plugging a dongle into the USB port that communicates with the wireless keyboard that the viewer uses. Many makes and models are available and all are plug n play so you just connect and go. Be careful though as some require replacement batteries while others use rechargeble.
A mouse can be used to control your HTPC set-up without the need for a keyboard, although for many a keyboard is a must for typing in search boxes etc. As with keyboards there are many wireless mice available that connect in the same way as a keyboard and give all the functionality of a mouse without wires.