I'd say Tampa is one. Some claim it's not because the streetcar doesn't collect enough at the fare box to turn a direct profit. However, no streetcar, light rail or expressway in this country does. However, Tampa's streetcar did help bring over $1 billion in new development to a distressed inner city community there, over a ten year period. To me, that equals fiscal success, in terms of increasing property taxes, building permits, generating new businesses, residents, etc. in an area of town where the infrastructure already exists (schools, parks, fire, police, roads, utilities, etc.).
Other good examples of sprawling sunbelt communities with successful starter lines include Memphis, Salt Lake City, Charlotte, Norfolk and Houston.