Howdy,
Euroreef CS6-3 or CS8-2. I have a CS6-3 on my 180, and it works perfectly. I don't know if you have ever seen one in action, but the column looks like white PVC when the pump is on. There are sooo many tiny little white bubbles that you can't tell the tube is clear acrlic until you put your face upto it.
I have heard the lifereef skimmers are excellent, but they usually require a fairly large pump. I like the Euroreef becuase it comes with a pump, a sedra, and they use alot less electricity.
I also have an AquaC EV150 on my 80g, and it works very well. You could use the EV200 for a 180g. The AquaC skimmers are also nice because they use smaller pumps.
Good luck,
Scott.