Ecchi

Fan Service is found in many anime, in many forms. When the service has a distinctly sexual slant to it, and it appears to be a major focus of the show, then it's safe to assume you're watching Ecchi.

"Ecchi" is used by English-speaking anime fans to refer to soft-core pornographic or sexually suggestive anime and manga. This is a western invention, as in Japanese, it is a catch-all term for all things sexual, not limited to porn and not really considered a "milder" term. The term "ecchi" in Japanese comes from the pronounciation of the letter "H" in English - "aitch" is rendered into Japanese syllabary as エッチ, which in turn is transliterated into the Roman alphabet as "ecchi". The letter "H" comes from the word "Hentai", but the term as currently used is not synonymous with Hentai.

The line between Ecchi and Hentai can be hard to draw at times. However, one good rule of thumb is, if it was aired on Japanese public TV at all, it probably wasn't Hentai. Ecchi usually features Barbie Doll Anatomy, or avoids nudity with lingering Panty Shots. Hentai, on the other hand, will usually show full frontal nudity in some explicit form, and full, intimate sex scenes. At its mildest, Ecchi is closer in spirit to shows like Three's Company and Are You Being Served?, full of Double Entendres, big misunderstandings, and sexual farce. At its most explicit, it is still more in the realm of HBO Presents than Vivid Video. Another good way to distinguish the two is if there are any animated sex scenes. If so, you have left this genre entirely.

To borrow an old saying, when it comes to sexual content, Ecchi is the sizzle; Hentai is the steak.

Possibly because sex is inherently funny, a large number of Ecchi series are comedies. Many start out as softer versions of actual hentai content (such as video games), while others may revert/graduate back to such if an OAV is released.

Anime and Manga

 * Amaenaideyo!!
 * B Gata H Kei
 * Battle Programmer Shirase
 * Baka to Test to Shoukanjuu
 * Boku wa Tomodachi ga Sukunai
 * Buttobi CPU could be considered a borderline case for either Ecchi or Hentai, though it is marketed primarily as the latter. It stands more or less in the same position as Ebichu—there's a lot of risqué material, but it's too funny to be a straightforward Hentai.
 * Change 123
 * Chobits
 * Chrono Crusade
 * Colorful
 * Cube×Cursed×Curious
 * DearS (Magical Girlfriend? Not necessarily ecchi. Magical sex slave? Ecchi.)
 * Elfen Lied — A subversion: the story as a whole is a drama/horror. Much of nudity is Fan Disservice and misleads the audience quite a lot.
 * Futari Ecchi
 * Gacha Gacha features plenty of boobs, panties and other lighthearted fetish material, there's even some nudity, although only limited to nipples.
 * Ghost in the Shell — Man-Machine Interface was pretty well fueled by this. The plot was not nearly as strong as the original manga and there seemed to be more panels featuring closeups of the Major's ass than anything else.
 * Godannar
 * Gravion
 * Grenadier
 * Hanasaku Iroha
 * Hanaukyo Maid Tai
 * Hand Maid May
 * He Is My Master
 * Highschool of the Dead features Gainaxing on girls being torn apart by zombies, a girl cracking open human skulls with a wooden sword while wearing nothing but an apron and a thong, and one particular gratuitous sequence of bouncing in Bullet Time.
 * High School D×D
 * Higurashi No Naku Koro Ki kira - these OVAs much more fanservice centered than the original series.
 * Hyakuen
 * Ikki Tousen
 * Inumimi
 * Is'' - manga about a guy who would really like to date a certain girl.
 * Jungle de Ikou!
 * Kanokon. So much hypersexuality in one half hour.
 * Kiss X Sis - A high school boy has two very aggressive sisters who are both vying for his affection. Don't worry, they're Not Blood Siblings of his.
 * Koihime Musou jumps between shameless pantyshotting and contriving to get the girls into as many compromising positions as possible, often lampshading it and complementing it with surprisingly classy dialogue and references.
 * Kyou Kara Maou
 * Ladies versus Butlers!
 * Love Hina (Less risque than the manga it was based on. Manga features lots of naked female flesh, albeit with absence of nipples and barbie-doll crotches, anime has them wrapped in towels or shown from behind)
 * Mahoromatic
 * Mahou Sensei Negima, by the same author as Love Hina.
 * Mai-Otome Zwei. The rest of the Mai Franchise is fairly heavy on the Fan Service but doesn't focus nearly as much on it.
 * Maicchingu Machiko Sensei was one of the Ur Examples—being a kids show that revolves around new and creative ways for the titular Machiko to lose her clothing and/or be sexually molested by her elementary school students.
 * Maria Holic
 * Mashiro-iro Symphony
 * Minami-ke
 * MM!
 * Musumet
 * My Lovely Ghost Kana
 * Nagasarete Airantou
 * Nana to Kaoru
 * Need a Girl
 * Ninin ga Shinobuden (Simultaneously parodies this and plays it straight.)
 * Omamori Himari.
 * Please Teacher, Onegai Twins, although these shows have a bit more serious content than most, especially the latter.
 * Ore no Imouto ga Konna ni Kawaii Wake ga Nai
 * Oruchuban Ebichu (While the show featured material that could be considered explicit, the simplistic art style and goofy premise kept it from being taken seriously as Hentai.)
 * Panty & Stocking with Garterbelt
 * Princess Lover
 * Popotan (anime)
 * Queen's Blade has no objection to showing nipples, and the proportions of the female characters cover every trope applicable to breasts.
 * Ranma ½
 * Rosario + Vampire (the anime; not so much in the manga)
 * Sekirei is a pretty ecchi manga and anime series... including giant breasts, nearly naked scenes and lots of nosebleeds from the main male character.
 * Shinkon Gattai Godannar
 * SHUFFLE!, one of the best examples of Cerebus Syndrome in the genre (harem comedy turns dramatic halfway into the series. Let's not even get started on Kaede Fuyou.
 * Sora no Otoshimono
 * Steel Angel Kurumi
 * Strike Witches
 * Tenchi Muyo!
 * Tengen Toppa Gurren Lagann - Guren Gakuenhen (The high school AU manga).
 * A case could certainly be made for the anime itself falling under this, especially Lagann-hen.
 * Tenjho Tenge
 * To Aru Majutsu no Index
 * They Are My Noble Masters.
 * To Love Ru (Try looking for even one manga chapter without gratuitous nudity and/or underwear shots. The anime adaptation even has nudity and fanservice in the OP, ED, and Eyecatches!)
 * Chapter 48 is an exception, believe it or not. It's probably the only one, too.
 * Training with Hinako is an OVA series that promotes healthy lifestyles by rewarding the viewer with ecchi imagery as they work their way through the exercise DVDs. Or, you can just skip the exercise with your DVD remote and go straight to the bouncing teenage anime mammaries and girl-on-girl bathtub groping. No-one will judge you any worse for it, but that will probably not make you healthier.
 * Ultimate Girls
 * Zero no Tsukaima
 * Underdog
 * Wagaya no Oinari-sama.
 * The Witchblade anime surely delights in showing Masane's... ample assets with VERY LITTLE covering them. However, it's in many ways a subversion - as the actual appearance is quite sexy, what's she doing is absolutely not.
 * Yomeiro Choice

Comic Books

 * The Animesque comic Empowered. Sex scenes galore, but Godiva Hair and Scenery Censor are flat-out abused.

Other

 * Hook+Ups, a company that makes graphics for skateboards and snowboards, as well as stickers. All their products feature a scantily-clad Animeesque girl, with "Hook+Ups" in silver Block Letters