I use a Pentax Digital Spotmeter. It's accurate, relatively small, very easy to use and very dependable. If the digital version is too pricey for you there is the older, larger analog Pentax Spotmeter V. Batteries are easy to find for either version. Just stay away from the older versions than the Spotmeter V because batteries can be hard or impossible to find.
Minolta and Soligor spotmeters are also said to be fine meters but I have no personal experience with them.