Hi bushygs,
There are numerous simulation tools are available in net. Each has its own advantages. To start with you can try "TINA Design Suite"
TINA Design Suite is a powerful yet affordable circuit simulation and PCB design software package for analyzing, designing, and real time testing of analog, digital, VHDL, MCU, and mixed electronic circuits and their PCB layouts. You can also analyze SMPS, RF, communication, and optoelectronic circuits; generate and debug MCU code using the integrated flowchart tool; and test microcontroller applications in a mixed circuit environment. A unique feature of TINA is that you can bring your circuit to life with the optional USB controlled TINALab II and LogiXplorer hardware, which turns your computer into a powerful, multifunction T&M instrument. Electrical engineers will find TINA an easy to use, high performance tool, while educators will welcome its unique features for the training environment.
you can get this software here
Analog, Digital, Symbolic, RF, VHDL, MCU Circuit Simulation & PCB Design
I have experimented with tina 6.0 and iam sure you can see the LED blinking here.
Explore their site othe useful softwares are available
One more software u may like in their website "Edision". link
Edison the Multimedia Lab for exploring electronics and electricity
It gives Real-time 3D graphics and lifelike 3D components will captivate your students as they build circuits in the real 3D world.
Hope it helps u...