'rAsAththi onna' of vaidhEki kAthirundhAL is the PJ song I love most. He had two more gems from the same movie, 'kAthirundhu kAthirundhu' solo and 'inRaikku Enintha AnandhamE' duet with VJ.

Other favourites (most of these were posted and discussed in jaiganes' 1000 songs thread) :

-vasantha kAlangaL (rayil payaNangaLil, MD - TR)
-vasantha kAla nathikaLilE (moonRu mudichchu, MSV)
-Adi veLLi thEdi unnai (with VJ, moonRu mudichchu, MSV)
-manjaL nilAvukku inRu orE sukam (with PS, muthaliravu, IR)
-mAnjOlaikkiLi thAno (kizhakkE pOgum rayil, IR)
-thavikkuthu thayangauthu oru manadhu (with SPS, nathiyaiththEdi vantha kadal, IR)
-chithirachchevvAnam sirikkakkaNdEn (kARRinilE varum geetham, IR)
-oru vAna vil pOlE (with SJ in KVG, IR)
-rAjAppoNNu adi vAdiyammA (ore muththam, IR)
-kAdhal mayakkam (with Sunantha, pudhumaippeN, IR)
-oothakkAththu veesaiyilE (with SJ, grAmaththu athyAyam, IR)