KL airport has an overnight hotel just off the airport car park. The rooms are tiny, and I mean tiny, but are fine if all you are wanting between flights is a bed. To get anything extra it costs, even if you want the air con on, but hey its budget.

As a bonus after leaving the airport, on the far side of the car park is a cafeteria. The food is basic but a lot of choice and great for the budget conscious. So we stopped for a feed.
The Tune Hotel also has a 7 eleven in the building.