Here’s one measure, from OpenSecrets.org
Based on contributions from PACs and individuals giving $200 or more, donations during the 2011–2012 election cycle
Sector: Finance/Insur/RealEst
Amount :: $96,283,676.00
Dems: 38.40%
Repubs: 54.50%
Sector: Other
Amount :: $61,118,388.00
Dems: 53.20%
Repubs: 42.30%
Sector: Misc Business
Amount :: $57,078,508.00
Dems: 45.70%
Repubs: 47.20%
Sector: Lawyers & Lobbyists
Amount :: $44,570,777.00
Dems: 67.00%
Repubs: 32.50%
Sector: Health
Amount :: $34,020,368.00
Dems: 43.80%
Repubs: 55.40%
Sector: Communic/Electronics
Amount :: $32,415,569.00
Dems: 50.30%
Repubs: 29.20%
Sector: Ideology/Single-Issue
Amount :: $29,670,275.00
Dems: 53.90%
Repubs: 44.90%
Sector: Energy/Nat Resource
Amount :: $20,478,171.00
Dems: 22.90%
Repubs: 76.70%
Sector: Construction
Amount :: $18,476,987.00
Dems: 25.80%
Repubs: 56.40%
Sector: Labor
Amount :: $15,562,921.00
Dems: 75.20%
Repubs: 12.20%
Sector: Agribusiness
Amount :: $14,030,191.00
Dems: 29.30%
Repubs: 68.80%
Sector: Transportation
Amount :: $13,012,124.00
Dems: 26.50%
Repubs: 70.50%
Sector: Defense
Amount :: $6,804,767.00
Dems: 38.30%
Repubs: 61.30%