Although this is cello-based, I found this website to be really informative. It shows the difference between sul tasto (on the fingerboard) with sul ponticello/sul pont (on the bridge), and gives demonstrations between the different styles.
Sul tasto produces a softer, less edgy tone.
Sul pont produces a raspy, edgy tone.
These can be ‘cancelled’ by notating ordinario (ord).
Rolen, R. (Unknown). Ponticello & Tasto Overview. Available: http://www.moderncellotechniques.com/bow-techniques/ponticello-tasto/ponticello-tasto-overview/. Last accessed 05/05/2016