Songs We Know:

• The Last Saskatchewan Pirate
• March of the Cambreadth
• No Nay Never- Shag Foreign Fighters
• Pills of White Mercury
• Green Grow the Rushes, O

Rounds We Know:

• Three Blind Mice and other Rounds
• Chiding Catch
• Hymn to the Russian Earth (debatable)

Songs We Know Bits Of: 

• Mingualay Boat Song
• Barrett's Privateers
• Ye Jacobites by Name
• Catalan Vengence
• Hope Eyrie(The Eagle has Landed)
• All for Me Grog
• Farewell to Tarwathie
• The Parting Glass
• Wild Rover

Songs We've Made Up:

• Let's Do It, Let's Go to War

Songs We'd Like To Know: 

• Lies I've told Virgins (actually called 'Three Biggest Lies' by David Allan Coe)
• We definitely don't know the correct words from even the little bit of this we do remember (Thank you Your Grace) 
• Serious Steel(Bringing the War Home)
• Black Powder and Alcohol
• Away day (Gaudete)

Songs Which Are Not Even Remotely Period That We Know:

• I am Cow (the song we are most likely to sing)
• Carrot Juice is Murder
• Down to the River to Pray
• Didnt Leave Nobody but the Baby
• Cows with Guns

Places To Learn Even More Songs:

Choral Public Domain Library: Includes sheet music and MIDI sound files for an astonishing number of choral works. Can browse by time period as well.

Musopen: Includes downloads of free recordings. Can browse by time period as well. Fewer works than the CPDL, but still nice for a listen.