Most of the tamil film music albums are monotonous nowadays.. with a 'kuthu' paattu, item number, duets, 'hero-worship' song and some senti ones. I have found a few albums quite unique in this sense..
1) Kadhal Desam: All the songs were by male singers; in all the songs, both the heroes, Abbas and Vineeth appeared. One of the singers, SPB, who sang a passionate song for both the heroes (Ennai kaanavillaiye) also acted as the heroine's father. And, I think it is the only movie so far in which AR Rahman has sung two full songs.
2) Snehithiye: Just opposite to Kaadhal Desam.. all female singers.
3) Rhythm: Each of the five songs had a theme based on five elements of nature.
4) Minsara Kanavu: 3 National awards for this single movie - Chithra, SPB and AR Rahman.
5) Hey, Nee Romba Azhaga Irukke: Five songs - each composed by different music directors (all debuting).