The major churches in Salzburg are within walking distance of the Center. Keep in mind that Austrian churches are not heated in the winter.  The weekend edition of the Salzburger Nachrichten (Lokalteil) publishes the times of religious services in various churches.
Dom (cathedral): 8:30, 10:00 and 11:30 am. The 10:00 am is a high mass with large choir and orchestra. They sing a different mass every Sunday. See the schedule in the narthex. Go there early to get a seat.
Franziskanerkirche (Franciscan church): Sat. 7 pm, Sun. 9:00, 10:30 am and 7 pm. The 9:00 am mass is the high mass with choir and orchestra. See the notice at the door for which music is scheduled for the following Sunday.
Dreifaltigkeitskirche (at Makartplatz): Sun. 10:00 am
St. Andrä (the local parish on our side of the river, across from the Schloss Mirabell): Sat. 6:00 pm, Sun. 8:30 , 10:00 am and 20:00 pm.
St. Peter Stiftskirche (St. Peter’s Archabbey): 9:00, 10:30 am. Some Sundays there is a choir and orchestra.
St. Sebastian (Linzergasse): Sat. 6:00 pm (old Latin Mass), Sun. 9:30 am (high Mass).
Evangelische Christuskirche (Protestant church along the river, on the Elisabethkai, behind the Schloss Mirabell): Sunday service in English at 11:00 am. Rev. Michael Spangler is the pastor of the American community.
Calvary Chapel Salzburg (Roitnerstrasse 9): English-speaking church service with German translation, Pastor: Ivan Ibbotson. Sundays at 10:00 am.