Depends on what level of control you want, and how much you want to spend..

At the lower end of both is the LightHouse from premium aquatics ($300).. limited number of outlets it can control, limited programmability. On the plus side, it has a nice web interface, and is made in the US.

Next in capability is the AquaController Jr. It's base price is $150, but you have to buy probes and x-10 modules, so it could end up costing more than the LightHouse. It also has more control and programmability.

For even more control, the discontinued AquaController II can be had used pretty cheaply.. more devices, more control.

Then the higher end starts.. the AquaController III / Pro ($500-$900 with various options and controls) It has more control, can be expanded to be used on multiple tanks, and has a bult-in ethernet port that provides a web interface.

There are others, but I don't have a lot of experience with them.

While I am biased, I prefer the Aquacontroller. This unit seems to give the user the most bang for the buck. More controllable outlets, more programming options and expandability.

However since you asked here is a list of controllers that I am aware of.
ReefKeeper 2 (http://www.digitalaquatics.com/index.html)
LightHouse (http://www.mcuresearch.com/)
AquaController (http://www.neptunesys.com)
Octopus 4000 (http://www.aquadyne.com/Product.htm)
Aquatronica (http://www.aquariumobsessed.com/)

Thank you both for your help. Time to dip into the kids college fund.

Tony,

I have the AC3, so far cannot find anything it will not due, other than have more than 24 timers.

If you need more than that look at the AC3 Pro

Glenn,
I was leaning toward that brand. I was considering the Jr. model. What options do you think that I should get with it? I am still new to reefing and don't know what I don't know. I would like the peace of mind knowing that the system is being monitored and controlled properly. Right now all I have is a thermometer. When I come home from work I frantically run past the wife and dogs to check the tank temperature and hope that the fan that is keeping the metal halide lights from boiling the tank is still working. Is anyone else going through this? I was looking on www.neptunesys.com.

What I did was set down and make a list of the things I would like to control, or know.

Lights, Fans, Heaters, return pump, skimmer pump, top off water, co2, etc..

Then when you know what you want to control, you can deside if you need a DC-8, DC-4 etc..
What I like about the AC3 is the ethernet port that is built in.

Tony that is the EXACT reason i bought mine. I was havin heat issues. At now with the timers and programming I can shut off things if that get to hot automattically.

Serk also got his controller for peace of mind after a problem popped up. In his case, he had a ph spike because his topoff water contains kalk. His program contains a statement like if ph > 8.3 then ATO off.

Steve allided to the fact that the AC line can do multiple actions based on conditions, instead of a single one. With the RK2 or the Lighthouse, your programming is limited (if temp > x, heater off or if ph < y then calcium reactor off) whereas the AC can do something like if temp > x, heater off; if temp > y light 1 off; if temp > z light 2 off.

I'll also jump on the Aquacontroller band wagon. I bought the AC3 for the integrated network functionality(web server and email alerts), ability to control 24 devices, and ease of programming(at least for me).

Yeah, if I was getting a controller as my only means of tank control, I'd probably go with an AC3... but for me, the majority of my control functions are handled by custom scripts I wrote on a Linux server, and the primary purpose of the controller was just as a means to get readings to the computer for it to act on, which is why I went with the cheaper, but far more limited, Lighthouse...

I have the AC jr. with a DC-8 on my new 75g and it is awesome. Nice bang for the buck. I'm gonna have to get another for my 1st tank (60g). Makes me wonder how it's made it almost a year without.

Thanks for all the input. I think that I have decided to go with the AC Jr. w/temp probe, serial port, Lab ph probe, and DC8 outlet. The cost is $ 316.40 less shipping from www.neptunesys.com. To be able to monitor my ORP I would have to upgrade to the AC III and purchase the Lab ORP probe. The cost would increase to $ 689.85 less shipping. Is it worth the $ 373 for this option? I am still new to reefing and don't know. I do have a lot invested in corals at this time(maybe not compared to you guys) and want the best for my tank without going overboard. I look forward to your input. Thanks again!!!

The main (But not necessarily only!) reason you'd want to monitor your ORP is if you plan to dose ozone. If you're not planning on using ozone, you're fine without monitoring ORP. If you are dosing ozone, or plan to, then being able to control the ozonizer vs. the ORP level of the tank is a must, IMHO...