The fine folks at DJ Intelligence collect song request data from thousands of events and make it publically available.

Here are some of their lists:

Bouquet Toss
Bridal Party
Bride + Father
Cake Cutting
First Dance
Garter Toss
Groom + Mother
Overall Top 200
Top 1950s
Top 1960s
Top 1970s
Top 1980s
Top 1990s
Top 2000s
Top 2010s