I've been using a Toyo 250 from
www.balances.com in the darkroom for a few years now, and I've been happy with it. It's a digital pocket scale with a capacity of 250g and reads to 0.1 g, which is enough for most darkroom uses. If you make your own fixer regularly or are mixing larger quantities of developer, you may want a second scale with a capacity of around 3 Kg.
Avoid really cheap scales, because they can be non-linear. Make sure your scale can be calibrated, and get a standard calibration weight of the appropriate size for the scale, if it doesn't come with one.