One of the most easiest corals to grow and take care of in a saltwater reef aquarium is the green or brown star polyps or if you want to get scientific, Pachyclavularia (genus). These corals are considered a beginners coral, they can be very forgiving when it comes to poor water quality. The star polyps are also very tolerant of both low light and intense light as well and are very tolerant of a wide range of current. These corals should be kept at normal saltwater reef tank parameters.
These corals do not need any additional dosing other then your weekly water change but can be sensitive to to some phosphate removing sponges (the ones that use aluminum oxide). In my experience as with other soft corals they seem to like a little bit of phosphate in the water however so does nuisance algae. You also do not have to directly feed star polyps, they are photosynthetic creatures that do not require additional feeding provided that you have ample lighting.
Green and Brown star polyps are often fast growing corals that are easy to propagate. The easiest method for this is to let them grow on top of rubble rock and then break or cut the piece of coral that grew on top of the rubble. I currently have five colonies spread throughout my reef tank just by using the above method.
Obtaining star polyps as you can imagine, is an easy task. You can find these corals at any reef club, ebay, or on online forums. The cheapest way is to simply go to a reef club and ask for a couple of frags, usually if you are starting out other reefers will give you a frag or two. Buyer beware though, some online sites demand up to thirty dollars for a frag of star polyps that is only one to two inches big.