By far the coolest phone / tablet app I've come across. EveryCircuit is a simple SPICE circuit design tool with a slick touch interface, shows voltage and current animations and more. This is no doubt the look and feel of circuit design tools for the future. Also could be a fun, easy way to learn or teach circuit technology.
From Android Market
"Features: + Animations of voltage waveforms and current flows+ Analog control knob adjusts circuit parameters+ Automatic wire routing+ Seamless DC and transient simulation+ Single play/pause button controls simulation+ Saving and loading of circuit schematic+ Mobile simulation engine built from ground-up+ Intuitive user interface+ No AdsComponents:+ Sources, signal generators+ Resistors, capacitors, inductors+ Diodes, Zener diodes, light emitting diodes (LED)+ MOS transistors (MOSFET)+ Bipolar junction transistors (BJT)+ Ideal operational amplifier (opamp)+ Digital logic gates, AND, OR, NOT, NAND, NOR, XOR, XNOR. Coming Soon: + Oscilloscope+ More components"