I'm using my MX5500 and it works great for my living room pc. I get no noticeable lag, and the range is good. More than anything I'm really impressed with the battery life. Keyboard uses AAs but the mouse is rechargeable and has its own charger stand. I use it for gaming on my plasma and I only put it on the charger once a week.
Been using this combo for nearly a year. I would recommend getting a half decent mouse pad though, it works on any non-glass surface, but using it on the couch cushions or the end tables seems to make the mouse have problems with accuracy.
Buy Logitech [920-000436] Logitech Cordless Desktop MX5500 Revolution
It's not cheap, but if you check Tiger Direct on occasion they seem to have it on sale for about 115$ every once in a while (which is kind of funny since their prices usually suck)