Which reminds me I haven't done a webcomics recommendations post in a while.
Red's Planet Aliens abduct a girl from earth -- and lots of other aliens from their planets -- before they crash on yet another planet. (I was wondering about this one for a time since the heroine seemed a bit too self-centered, but she shows more than that after a bit.
Cucumber Quest A parody of fantasy video games. Also funny if you only read books; the tropes are familiar enough.
Far Out. Robots in the Wild West!!!! An all-robot Wild West at that. Amusing little sketches of robotic life between the plot and the drama.
Impure Blood A fantasy revolving about a search for the last of the race called the Ancients. It opens with the rescue of a half-Ancient gladiator from the arena. Filled with secrets and drama.
Freefall Fun and philosophy, with robots, a squid-like alien and spaceship captain, and an intelligent anthromorphic wolf engineer
Order of the Stick Comedy! Adventure! In a D&D universe! A group of adventurers formed because their leader had to fulfill his father's death oath discover they are involved in a far more crucial matter.
Rusty & Co Comedy! Adventure! In a D&D universe! Three monsters realized who had the good deal and took up the life of adventurers!
The Specialists Superheroes in World War II-- a war dragged out years longer than in ours, because of German superheroes.
Bird Boy. A boy -- a clumsy boy -- stumbles on something in the forest. Something perhaps mythic in nature.
Gunnerkrigg Court A tale of a very, very, very strange school.
Erstwhile Tales from the Brothers Grimm.