Watts Up is good (I have it), but the Hyperion E-Meter is king. Tach, wattmeter, and computer hookup in one package. I would have bought it, but it came out after I bought the Watts Up. Astro lacks features. Medusa is pretty good, but it is very large, does have computer interface, but doesn't have amp_peak and volt_min, which makes wattmetering more dangerous.

Voltmeter? If you mean a digital multimeter, I went with the Fluke 81438 sold on ebay for ~$80 shipped. It is a 6000 count and current generation, and I love mine. I bought a calibration chip and found it read 4.999V on a 5±0.001V source.