Take a look here http://arduino.com.au/Simulator-for-Arduino.html
and let us know what you think. This Simulator only simulates the Arduino board so there is no option of adding resistors - Virtual Breadboard may allow that but there are mixed reviews for this and it costs somewhere around $29 from memory. With Servos, we just use an analog output which progressively becomes a darker shade of red. Thermonuclear reactors are best left for Tepco - those guys can get these happening without doing anything.
The Simulator for Arduino has just been upgraded to v0.97B for Pro Users and there are many fixes and improvements - Free Version upgrade available now - the free version has a 30s delay on opening a sketch (increments by 1s each time) and is code limited to 100 lines. Most of the Official Arduino sketches are included and there are many user sketches sent in for testing. Almost 850 Pro Users so far this year.
With the other Simulators, the Schogini iPhone app is pretty useless - I think the only change allowed is to change the delay between LEDs coming on. Looks good and works well as a training video but not really a learning tool. Had a quick look at Emulare but looked too hard to get going and not many people use 4 Arduino boards at the same time - also Emulare simulate AVR code not the special functions used by Arduino so not really an Arduino Simulator at all.
While the Simulator for Arduino is not perfect, it does have some great features such as auto opening the Serial Monitor and being able to step into custom library .h and .cpp files, as well as changing the font for the sketch by selecting Edit. Looking at the list of topics, it looks like our Simulator for Arduino may be behind some of the last few requests for suggestions on this forum.