Children. You can find little kids here in SL…or at least, avatars who look and act like little kids. This is, as I’ve said (Adults and Kids in Second Life), harmless roleplay, as long as the child avatar doesn’t participate in sexual activities. If you want to explore your inner child, one of my favorite places is Livingtree: http://maps.secondlife.com/secondlife/Livingtree/192/140/24
Nekos. The typical Neko is a girl, often goth-girl, with cat ears and tail, although you’ll sometimes see male Nekos as well. Nekos originated with Japanese anime. Nekos partake of both human and feline characteristics and behaviors. Some Nekos are shape-changers, having a fully human form, a half cat/half human form, and possibly a full feline form. People with Neko parts may be very much into the Neko scene and character, or may just be wearing the ears and tail as a cute fashion statement. Try: http://maps.secondlife.com/secondlife/Mirinae/195/32/39
Furries. A typical Furry avatar looks like a Neko who’s taken things a step further. They generally have an animal head, paws, and a furry body, although their shape is humanoid. However, Furries may also be shape-changers and have a fully-animal form. Furries, like Nekos, are an import from Real Life. People into the furry phenomenon go to real life conventions called “furmeets” and wear furry costumes. There is a presumption on the part of many people that male furries are gay in Real Life. Not being a Furry, or involved in that subculture, I can’t comment on the truth or falsity of that presumption. All I know is that most of the furries I’ve met have been very nice people. Try: http://maps.secondlife.com/secondlife/Yarmouth/195/173/29
Tinies. Think of a teddy bear, or other cute and cuddly stuffed animal. Tinies are about the only subculture I can think of that doesn’t have a clear antecedent in Real Life. (See "Badgers? We Don' Need No Steenking Badgers") Visit Raglan Shire to meet (or be!) a Tiny. http://maps.secondlife.com/secondlife/Raglan%20Shire/150/177/23
Mers. Some people like to be mermaids or mer-men, and there are whole sims devoted to mer roleplay. I have a couple of mermaid outfits and a nice mermaid AO. It’s fun to wear a tail and dance in three dimensions under the sea. http://maps.secondlife.com/secondlife/Neverdie/34/18/3
Dragons. There are many sorts of animal avatars, and several have their own communities…but dragons are perhaps the most impressive. Those who like to be dragons have a couple of roleplay areas. Check out: Grendel's Children or Seawolf Dragons for avatars. For roleplay, try Isle of Wyrms.
Gor. There are several Gorean regions, where aficionados re-create their versions of the male-dominated society described in the popular fantasy series by John Norman. Not my cup o’tea, but if you want to try a society where the, um, traditional male and female roles are carried to their extremes, you might give it a look.
Dominance and Submission, BDSM. D/s takes many forms and variations, from the mild to the stomach-turning extreme, and from the strictly mental to the physical. Fortunately for the extremists, in SL you can’t actually be physically harmed. SL is a relatively safe place to experiment with these “alternative lifestyle choices”. Nevertheless, do exercise caution. Some players in these realms are extremely subtle and accomplished mental and emotional manipulators. There are so many places you can find this, I haven't included any landmarks.
Steampunk. This is a new genre in science fiction. The basic idea is a culture set back in time over 100 years. The technology is that described by, say, Jules Verne…based on steam power and clockwork (and maybe a bit of Mary Shelly’s biological reanimations), Mad Science co-exists with cultured gentlemen and ladies in Victorian garb. Caledon and its allied regions (collectively known as the Steamlands) are wonderful and whimsical places. In addition to Second Life steampunk locations, check out this wonderful webcomic: http://www.girlgeniusonline.com/comic.php
Vampires. And Lycans (shapeshifters) too. Many who participate in this subculture also play the game “Bloodlines” or similar systems to “keep score”. If you get an unsolicited bite request from a Bloodlines player, decline it (unless, of course, you WANT to be bitten). If you don’t want to be bothered by vampires, get a free Garlic Necklace from theMarketplace to immunize yourself. If you DO favor Bloodlines and vampires, check out http://maps.secondlife.com/secondlife/Liquid%20Designs/122/126/239
Samurai. If you like Japanese-style sword combat, there are weapons and a combat system specifically designed for it. If you’re really into it, there is a website you can join to see how you rank against others: http://www.combatsi.com/e107/news.php
Medieval. These folks have a different combat system, and fight with Western style weapons. There are also many beautiful outfits, and places to show them off. The Avilion sims are a good example.
Science Fiction. There are roleplay areas based on several popular science fiction “universes”, including Star Trek, Star Wars, Stargate, and Avatar.
There are others, too…If you are a member of, say, a Fae community or a hobbit village or some other group I’ve left out, my apologies, and please feel free to leave a comment here!