The best bang for the buck DC clamp meters are Extech. I have the 380947 true RMS meter. It has a 40A DC range that will read with a .01A resolution which is good for measuring single strings of PV. It's other DC range is 400A. DO NOT buy a clamp on meter with only a 400A DC range since you will not have enough resolution for typical solar work. A lot of clamp meters have more sensative AC ranges than the DC ranges so look carefully.
The 380941 has 40A and 200A plus voltage ranges but I prefer a seperate DVM for voltage. Most of my DVMs are Fluke but I also have Beckman, Extech, Tektronix and Radio Shack.
The 380942 clamp meter has 4A and 30A DC ranges so it has .001A resolution but may not have high enough range for multiple parallel strings. (my array is over 35 amps peak)
Here is the data sheet on some of the Extech clamp meters:
http://www.extech.com/instrument/produc ... 42_947.pdf
I think my IR thermometer is a Raytek. It has a LASER pointer that is good for playing with the cats (alternate winter heat sources, also called Kitty Thermal Units)
Here is a solar irradiance sensor that uses an external meter:
http://www.davisnet.com/product_documen ... or_std.pdf