Saltwater aquarium
you will definetly need a protein skimmer if you have any invertebrates. I prefer a skimmer as the first line of defense in filtering a tank. You don't have to wait for the fish crap to go through the whole degratiion process. This means there will be less nitrites, nitrates to worry about. you will stress your ecosystem and your fish less with a skimmer.
I second s2kfanatics advice, go to reefcentral.com, reefs.org, reefkeeping.com, advancedaquarist.com, wetwebmedia.com and do plenty of reading and planning before you even begin adding any fish or inverts to the tank. Its an amazing hobby!

Here's a picture of one of my tanks:
Here's a picture of one of my tanks:




