i was at dominican republic last january and i used siutratural taxi services to make a trip to samana and others spot at dominican republic. they gave me a very good service, with good rates and the taxi's driver are very kind. i recommend you take taxis siutratural if you go to D.R.
post: if you don't have cash and you want travel around D.R dont worry, they accept credi cards. and their vehicles has GPS.