I've been using a logitech EX-111 combo since about a year now. The combo works on 27Mhz RF. The mouse is powered by 2 AA alkaline cells and the keyboard by 2 AAA alkaline cells.
The mouse batteries need replacement every 1 - 1.5 months which is a little annoying but the batteries are drained well esp. indian duracell batteries. Foreign duracell and energiser batteries have some left over charge which makes me wanna keep them. So I prefer indian duracells now.
The keyboard however goes a good 6-8 months without a replacement.
I've even used it for playing games like FEAR and FarCry. I don't think avid gamers would like the response but for me, it's ok.
The wireless transmitter is connected to the PS/2 mouse and keyboard ports of your mobo. It has some wire length between the connectors and the unit which you can bundle up and tie with a band. I would've really liked it to be USB driven or at least not have the excess wire of the transmitter unit but I'm ok with the PS/2 thing also.