Wireless Sensor Networks Simulation Environments

I have been searching for simulators appropriate for Wireless Sensor Networks, and found following simulators reasonable enough for simulating WSNs:

• NS2: This simulator doesn't provide WSNs' simulations, in its original form. Different patches although are available for simulating WSNs, e.g., NS2-MIUN, NRL, Mannasim.
• OMNet++: This simulator is comparatively easy to learn. Moreover, it provides drag-n-drop based GUI for designing network. For simulating WSNs, it has components Castalia, MF, MiXiM.