For Windows you can use Kismet, might be a bit less easy to play with like netstumbler, but it records all the APs and all the clients, their beacons and so on.
Also you can export its XML files to several other scripts and programs to get better representation then netstumbler and inssider.
In Linux best answer is aircrack suite: run airodump-ng with the right flags on monitor mode enabled card.
Your screen will be divided into two groups, in the top part you'll see all the AP's your card can see, and at the bottom part of the screen you'll see list of clients, where connected clients will have to their left the mac address of the AP they are connected to.
airmon-ng start wlan0 && airodump-ng mon0
where wlan0 is your wifi card
(although just airodump-ng wlan0 will work too)
and of course kismet will work here too.