The below map shows my plan for the Bangalore Commuter Rail Service.
Some of the routes which I believe would do good are as follows :
Bangalore City - Kolar via Whitefield and Hosakote ( The Whitefield - Kolar railway line which is still under construction is expected to connect the major industrial hub and the residential areas along the line, besides the Volvo factory in Tavarekere en route)
Bangalore City - Kolar Gold Fields via Whitefield and Bangarpet which is a major town in the state.
Bangalore City - Tumkur via Yeshwantpur and Nelamangala
Bangalore City - Kunigal via Nelamangala
Bangalore City - Chikballapur via Yelahanka and Devanahalli ( this under-utilized route provides connectivity to Nandi Hills as well )
Bangalore City - Gauribidanur via Yelahanka and Dodballapur ( Gauribidanur is the last of major towns in Karnataka en route to Hindupur )
Bangalore City - Anekal via Byappanhalli and Sarjapur road
Bangalore City - Kanakapura via Kengeri ( as it is not possible not to lay any more railway lines in the crowded areas of the city like Banashankari and Basavanagudi )
Bangalore City - Channapatna via Kengeri, Bidadi and Kengeri
Bangalore City - Magadi ( a new line needs to be connected for this either from the Nagarbhavi area in the city or Yeshwantpur for this. When completed this would benefit a large number of people thereby decongesting the busy Magadi Road.
The above plan also supports the idea of having more railway terminii outskirts of the city as presently the two railway stations at Bangalore City and Yeshwantpur are more than just saturated. Besides working out to be cheaper, the commuter rail system aids the passengers to carry more baggage unlike the metro (which is expensive due to the air-conditioning facility) where there an upper limit has been imposed on the weight of the permissible baggage.