For showers 6 feet in length or longer, a sliding glass door is an excellent solution. Typically, you'll have a glass front to the shower, with a roughly 3-foot glass section at one end that hangs on a track and slides back behind the other side when you open it. The advantage is that when it's closed, it's sealed completely, allowing no water spray to find its way out. The disadvantage is that the metal tracks can be hard to get at to clean. Use a scrub brush on a long handle.
If you don't have the space for a sliding shower door, get a door the swings out. These generally close with a standard latch or magnet. The seal isn't as tight as with a sliding glass door, but you don't have those metal tracks to contend with, and you don't need extra length on the shower wall to give it somewhere to slide. Also, many swinging glass shower doors are frameless--no metal around them like sliding doors, just tempered glass--which is far less intrusive, visually. If your bathroom is too small for a full door to swing out, look at a set of half-width doors that meet in the middle.
One of the best shower door setups is to have no door at all. This will only work if your shower area is fairly large, and can be positioned so that the doorway doesn't open your shower area directly into the room, but first rounds a corner or cove, to prevent water spray in the bathroom area. A perfect setup is an angled entry, in which you step through one small area and round a corner before stepping through the shower doorway itself. Make sure you have a "curb" at the bottom of the doorway, and position the shower head as far as you can from it.