IndianScreen.com, maintained by The Classic Movie Club based in the USA has a sizeable collection of old classic Hindi songs available for download and that too for free (legality of the download is has to be ascertained by you). You can also purchase cassettes (cassettes?) of songs from their collection (50,000 songs) for $3 a piece.
The movie club is also into preservation of old films and music, primarily 78rpm records. But there is a catch (as always), they keep on refreshing the list of songs available for download every Wednesday and remove the previous items. Therefore at a given time there might not be more than 100 songs available. Moreover the files (in MP3 format) have a bit rate of only 16kbps and therefore the file sizes are usually sub 500 KB, but the quality is satisfactory for personal non-fussy listening.
A good place for lovers of old Hindi film music with many forgotten gems lying around. Only the layout is very amateurish.