I have been to Messini a number of times. It stands out in my mind as a beacon on the Danforth...amongst the touristy and overpriced Greek food spots.
I almost always order a Combo with a friend. The Combo gets you 2 sandwiches, a salad, and fries. I recommend chicken gyro sandwich, Greek salad (the type with no lettuce!) and Greek fries. Greek fries come with feta baked on top...mmm...
The combo costs around $16. So, two people can eat really delicious food - and be totally STUFFED - for about $20.
The catch is that there is often a line-up to get a table. You can also do take-out there, which is awesome, but the containers spill so be careful if you go that route. I would also warn against going here for a "nice" dinner. This is the type of place you go after work, when you want your food to come quickly! And that's exactly why I love it.