Electrical analysis tools.

Wire Sizing ...  
Ampacity and voltage drop tables 
The two main things in picking wire size are: 1) don't exceed the maximum current carrying (ampacity) of the wire, and 2) don't have an excessive voltage drop along the wire. I find these two tables helpful in a lot of cases to check for ampacity and for voltage drop. 
Good Voltage Drop Calculator from Calculator.net ...

A good voltage drop calculator for any voltage DC or AC. Also wire properties, resistance, ampacity table for copper wire. 
Voltage Drop Calculator, Nick Degaggis 
Very
handy wire size calculator.

Another good voltage drop
calculator
http://www.csgnetwork.com/voltagedropcalc.html

Another very nice calculator. 
Various wire sizing and
maximum amperage tools, tables, calculators, and wire application data: Another wire table for AWG that includes resistance per 100
ft and much more.
And another from
Northern Arizona Wind & Sun 

PV Array Sizing  
PVWatts  A Performance Calculator for GridConnected PV Systems From NREL http://rredc.nrel.gov/solar/calculators/PVWATTS/ This is a really useful tool. 
An easy calculator you can use to find out how
much power you will get from a PV installation in your area. It calculates PV system performance based on hour by hour records for sun in your area. Version 1 is very easy to use, and works worldwide. 
PV wiring recommended distances and
currents chart.

Recommended distances and currents for 2% voltage drop in low voltage PV circuits. 
Electric Motor Tools  
http://www.teicontrols.com/motoramp.html

Approximate motor current draw at full load. 