The following is an extract of the current timetable for the long distance coach services operated by http://www.internorte.pt/ between Lisbon - Porto - Vigo - La Coruna - Santiago da Compostela. Internorte do not have an online interactive timetable. This is an extract from the downloadable pdf.
(Click on the image to enlarge:)
Important Addendum:
Many thanks to Cubsur of www.algarvebus.info for pointing out that the Spanish bus company www.autna.es also operate four daily services (Monday to Saturday) between Porto,Porto Airport and Vigo and v/v. On their website main page, click on Servicios then Lineas Regulares for the timetable.