There alot I would have loved more eps toXD Elfin Lied is at the top of my list and trinity blood. There are others too, but too long of a post to list them here...lmao
Mononoke and Ga-Rei Zero. I would like it if Ga-Rei included the story from the manga instead of it just being a prelude. Seriously, why do some of the best animes only have 12 some odd episodes in them?
I gotta say:
- History's Greatest Disciple Kenichi
- D.Gray-Man
- Darker Than Blan & S2(Ryuusei No Gemini)
- Code Geass & R2 (OMG THEY MIGHT B RELEASING A NEW SERIES)
Gantz needed to remove the last five episodes and continue to follow the manga. It was just starting to get good after the temple battle and the animation ruined it. I never watch the last 5 episodes anymore.
Black Lagoon needs more episodes though. High School of the Dead will as well since its slated for 12 episodes and is moving really slow through the series. Maybe there will be a second season.
Gundam 0083 is really one of the only anime I can think of that could fit more of a story into it, and have more episodes, without dragging itself down in some way. At most, 13 more would be great.
Oh, and also FLCL. I could easily see more episodes for that one, and would love it.