This is a review for the vegetarian/vegan Earth Cafe near the Djemma El Fnaa square. As other users have pointed out, the easiest way to find Earth Cafe is to locate the Waha Cafe on the southern side of the square. Take the little street to the left of it and walk a few minutes. You'll see signs pointing to the Earth cafe.
My friend (omnivore) and I (vegan) came here twice because it was easy. My friend was very pleased with her meals (her first forays into vegan/vegetarian dining). I thought it was good but honestly I've had better. Having said that, the meals were more than satisfactory and the service was good. Staff speaks English and French.
I had the veggie burger (no bread, patties were tasty but not that filling), the filo vegetable pocket with tomatoes (delicious and filling) and a carrot-ginger juice (good). Most dishes were about 70 MAD (=7 EUR).
Overall, a good veg café, makes eating very easy in Marrakech. I'm glad they're there. The owner is a Moroccan who lives in Casablanca. There's also an Earth Cafe in London.
For those who say that eating vegan in Morocco is difficult - I suppose it depends on your circumstances (i.e. large city vs small village) but I respectfully disagree. I had no problem eating vegetable couscous dishes in sit-down traditional restaurants (I was assured the broth was vegetable-based and it appeared so). Just explain that you don't eat any animal products. The only person to react in a somewhat shocked manner was a French riad owner in Marrakesh. You could also try vegetable tajine and ask for veggie starters (olives, carrots with cumin, potatoes, aubergines etc).Pros: vegan options, cheap, nice service
Cons: building is a bit run-down