The following list has no particular order. In the order of what comes to my mind! :-)
Kireedom
This movie makes me disturbed. Period. The fate of Sethumadhavan can occur to any honest person. A man who loses everything loves due to no fault of his. This songs sums it all.
Spadikam
If the protagonist in Kireedom is a result of societal issues, the protagonist in Spadikam is a result of bad parenting. One of the best action films in Malayalam, which curiously is also one of the best family drama.
Aaram Thampuran
My favourite scenes in the movie are the combination scenes involving Manju Warrier and Mohanlal. Smooth talking and witty dialogues. Exceptional facial expressions. The best of Mohanlal comes out when he acts with other class actors. Sadly, this is missing these days! I wonder how better Bhramaram would have been, if others could act worth a salt!
Thoovanathumbikal
Even though this movie shines mainly because of the beautiful writing and skillful direction of Padmarajan, you cannot deny the class of Mohanlal's acting. He slipped easily into the role of a simple villager, later revealed to be not-so-simple. His scenes with Sumalatha are the best in the movie.
Dasaradham
If you don't have tears after watching this, you can be sure that you have no heart. This is the best scene from the movie.
Adhipan
The best drunk Mohanlal scene. He is the best actor when it comes to portraying drunk characters. Natural and very endearing! No wonder we Malayalees like to drink!
Devasuram
A landmark movie in the landscape of Malayalam commercial cinema. Especially since it spawned a series of good and terrible superman movies. Mangalasheri Neelakantan will live on as "the man" of Malayalam cinema for a long time.
Summer in Bethlehem
The movie is peppy and smart, but looks to taper of into a glum, emotional drama until Mohanlal steps in taking you by surprise. He appears on screen for less than 8 minutes. But the impact is so big that you forget everybody else and giving the movie a satisfactory ending.
Nadodikkaattu
No list is complete without the late eighties comedy masterpiece Nadodikaattu and its sequel. You still laugh just thinking about the scenes. The dialogues from the movie has become part and parcel of our language.
Manichithrathaazhu
Mohanlal plays the role of eccentric doctor to perfection. The way his expressions and body language change is fascinating.
Making a list of Mohanlal's performances is akin to finding a needle in the haystack. This is not a top ten list. Just a list of ten! Here is another list by Brijesh Nair which features a few other (better?) performances.
Mohanlal movies I am looking forward to are with Roshan Andrews and Unnai Pol Oruvan with Kamal Haasan.
Share your favourite performances as well!