QCAD: Quantum circuit emulator
QCAD is a {surprisingly!} windows-based environment for quantum computing simulation which helps designing circuits and simulating them. Developed by Hiroshi Watanabe Masaru Suzuki and Junnosuke Yamazaki at University of Tokoyo and Nagoya University.
Extremely useful tool for designing Quantum circuits using graphical user interface (GUI). The designed cricuits can also be exported as EPS (Encapsulated Postscript) for use with LaTeX. I have not tried exporting the circuits but it does sound very useful.
Quantum Computer Emulator (QCE)
QCE is a software tool that emulates various hardware designs of Quantum Computers. QCE simulates the physical processes that govern the operation of a hardware quantum processor, strictly according to the laws of quantum mechanics. QCE also provides an environment to debug and execute quantum algorithms under realistic experimental conditions. The software consists of a Graphical User Interface (GUI) and the simulator itself. Developed and maintained by Zernike Institute for Advanced Materials, University of Groningen.
QCE runs smoothly on Windows XP and is known to support Windows 98/NT/2000/ME/XP environment. It gives a detailed exposition is given of the implementation of the CNOT and the To oli gate, the quantum Fourier transform, Grover's database search algorithm, Shor's algorithm, and more.
A paper titled "QCE: A Simulator for Quantum Computer Hardware" by K.F.L. Michielsen and H.A. De Raedt offers detailed information regarding QCE although the paper could have more clearer snapshots of the emulator in action.
jQuantum - Quantum Computer Simulation Applet
jQuantum is a quantum computer simulator. It simulates the implementation of quantum circuits on a small quantum register up to about 15 qubits. Its main intention is to create images—images which may help to learn and understand quantum circuits, and which perhaps will serve as building blocks for inventing new quantum algorithms. Hosted and supported by South Westphalia University of Applied Sciences.