I use the "Pocket Light Meter" app on iphone. I like it well enough.

For a decent cheap light meter (and one that fits with the vintage TLR aesthetic), a Gossen Luna is pretty solid. They even meter low better than most modern light meters. The only catch is they use mercury-cell batteries that don't exist any more. But it has a modern replacement called a "wein cell".

http://www.keh.com/camera/Light-Meters-Light-and-Exposure-Meters/1/sku-GM709990320290?r=FE

http://www.amazon.com/WeinCell-MRB625-Replacement-Battery-PX625/dp/B00009VQJ7

It is not necessary. A PX625A works well. A Wein cell is available if you want a 1.35V replacement. https://www.amazon.com/WeinCell-MRB625-Replacement-Battery-PX625/dp/B00009VQJ7