Visual novels as a medium probably have the ratio of adult material to safe material inverted compared to most other media. That is to say that unlike everything else, the majority of visual novels are 18+. Of course, that doesn't really quite matter so much because the number of visual novels that are available in English (legally or not) is similarly minuscule. After narrowing down the visual novels that are worth playing and safe, it's probably pretty easy to just give a list of them.
Of course, finding that list is hard because visual novel players are typically okay with 18+ stuff. They might not like it (I know a lot of people who complain about it in otherwise excellent games), but they put up with it. Clearly we're not comfortable with doing that here. Finding that list is hard also because there are way more fan translated VNs than there are officially released ones, which is probably in the single digit range.
As alluded to by Atria, the most popular of the 18+ visual novels have 18+ content only because they were created during a time when the thinking was that good writing wasn't enough to get people to buy a game, so they had to throw in 18+ scenes to entice the audience. This made it pretty easy to gut those scenes out once developers realized that people liked the games because of their stories.
An important correction, though: Key's games do not all have both 18+ and all ages editions. CLANNAD, Planetarian, and Rewrite have never had 18+ editions, while Tomoyo After and Kud Wafter have no all ages editions.
So what all ages English visual novels are there?
For completion's sake, you could argue that the Ace Attorney series are visual novels. I don't know if they are, but they're there if that's what floats your boat.
Arguably the most famous are 07th Expansion's When They Cry horror series. Mangagamer has officially licensed and is releasing Higurashi no Naku Koro ni, while The Witch Hunt releases unofficial translation patches for Umineko no Naku Koro ni with series creator Ryukishi07's blessing. A fan translation patch for Higanbana no Saku Yoru ni is in the works.
Ever 17 is one of the few big officially licensed visual novels, but the company responsible for it died years ago. Remember 11 is a visual novel from the same series and has a fan translation. And curiously enough, the staff behind Ever 17 went on to create a DS visual novel by the name of 999: Nine Hours, Nine Persons, Nine Doors, which is also available in North America.
As for Key games, both CLANNAD and Planetarian have fan translations. This is funny because Planetarian has no choices, while CLANNAD is one of the hardest visual novels I've ever played. The all ages version of Little Busters! is being worked on as well.
Both narcissu and narcissu -Side 2nd- are free visual novels that have received fan translations.
5pb/Nitro+'s collaborations have all been all ages. Chaos;Head has a finished fan translation, while Steins;Gate has a fan translation that's being worked on.
I'm not too up to date on news about otome games, but I do know that at least one part of Starry Sky has a fan translation done.
Finally, one that's often overlooked is a little known visual novel called Symphonic Rain. This one has a fan translation.
In the future, I'd imagine Rewrite, Key's latest game, and Mahou Tsukai no Yoru, TYPE-MOON's new game that's been delayed forever, will be getting fan translations. Both are all ages.
There are also a few games that have fan translations where the patch installer gives you the option to remove the 18+ scenes. I believe TYPE-MOON's Tsukihime is one of those games, and if I recall correctly, Flying Shine's Cross†Channel is too.