Nowadays, wireless technology has come very far, and there isn't any lag (with semi-new equipment) of mice and keyboards. I would suggest getting Logitech stuff, because I have had two sets of wireless combos from them (one top-of-the-line and one bottom-of-theline) and they both are very good.
I currently have the MX3100 Combo from Logitech, which comes with the MX1000 Laser Mouse and the MX3000 Keyboard. They are really amazing, however, it costs ~$120.
I also would suggest getting a mouse that uses Fast RF technology, because it is extremely fast and is (in the MX1000's case) the same as a USB corded mouse.
(Oh, and the MX1000 doesn't require batteries, it charges at a base station which is really nice. And, the keyboard batteries pretty much never run out.)