Light meter
Light meter
Well, it's really a question of the kind of shooting and control you're looking for. If you're shooting on video, the old Sekonic Studio Deluxe I or II is a great old reliable war horse. If you're shooting film, you really almost need three meters. An incident meter (the Sekonic), a spot meter and a color temperature meter. Film is unforgiving and there's only so much you can do to correct it in post and it's highly advised that you get the proper exposure in the field. For the spot meter, the Pentax Spotmeter V is one of the best ones out there. For a color temperature meter, you have several choices; the Minolta Color Meter II, IIIF or the Gossen Color Pro 2F and 3F.
Why the spot meter? It will save your butt every time you're wondering if something's going to blow out in your frame with the stock and stop you're shooting. Plus, it can save you from having to do an incident read everywhere on the set. With the spot, you can stand next to your camera and get reflective readings quickly.
Why the color meter? Color control. It's best not to let any colors get more than 1500 Kelvin out of your balance. If you're shooting on tungsten balanced film and your color is hitting close to 4K, you're in trouble and things are going to start looking blue and your shadows start to wash out. If you're shooting on daylight balanced film and your temp starts dropping down below 5200 K, your color is going to start looking orange and your blacks will start getting muddled.
