There are actually a lot of these aside from SAO, Log Horizon, and .hack//. Even if they don't use the stuck in an MMO shtick. For example:
Master of Epic : The Animation Age
This is kind of like a huge infomercial / improv comedy anime based on the MMO Master of Epic. By this I mean there is no coherent plot to the show. There are just a bunch of small comedy segments that are meant to entertain you while also educating you about the game's back story and mechanics.
The funniest part of this anime is probably that they have a segment that is a group of 5 lolis who run around the PVP zone just randomly PKing people.
This one is sort of more like Digimon meets Accel World. There is an extremely popular fighting game called Dragon Drive where the players raise and customize their dragons and then participate in tournaments. One day a few of the players get pulled into an alternate dimension / fantasy world where their dragons are real. As far as the characters go, they are more like Naruto / Reborn than they are like SAO, LH, or .hack//.
There actually have been animes that while they are not inherently about being trapped in an MMO or even based on an MMO do have such arcs.
Hunter x Hunter - Greed Island-
: I think it is the 4th arc in Hunter x Hunter, Gon and Killua end up in a sort of SAO situation while searching for Gon's dad.
Tsubasa Chronicle - S1
: I forget the actual episodes but mid season 1 / late season 1, one of the worlds they visit is actually a VR MMO run by the company from Angelic Layer / Chobits.
And I will put this in spoiler, but there are actually 3 series I know of ; 2 mangas and 1 video game, where the plot twist is that the entire story actually took place in a VR MMO the entire time.
Star Ocean Till the End of Time
: It turns out that all of your characters are actually just NPCs in a very advanced VR MMO. Near the end of the game you find a way to manifest yourselves in the 'real world.'
Sora no Otoshi-mono / Heaven's Lost Property
: The Sky people are actually a race of technologically advanced people who have basically reached godhood through their technological advances. After reaching godhood they became incredibly bored, and the entire world is actually just a matrix style game they have created for themselves.
: The main character Ginji is the only real human, he has been trapped in a virtual world through the entire series. It's made evident at the end.
Feel free to comment / add your own MMO related anime/manga.
I've Got Friends on the Other Side
druaga sword/aegis of uruk
His Holiness Optimus Maximus Decimus Meridius Colossus Nemesis Nexus Genesis