+1 from me as well.
It's somewhat short on components; it's mainly intended to support Linear Technology's devices. But it's easy to use and works well.
Chris (CDRIVE) uses Tina, available from http://www.ti.com.
+1 for LTSpice. Generally easy to use and has fairly accurate models built-in. If you know a little SPICE, you can make and program your own components and make them accurate to reality.