Successes

These are amounts I've collected.
$21.00 insurance refund
$27.75 bank overcharge
3.95 bank service charge refund
$120. neighbor
$152.64 gym
$325. landlord
$500. client
$795. landlord
$1500.
hotel
$2,631.60 client's boyfriend
$28.50 client
Total: $6105.44

These are some I am either about to go after, or am in the early stages of pursuing.
$19 pharmacist
√$20.13 property manager
$22 client
$20 client
$30 plumber
$100 magazine editor
$150 dentist
$188 dentist
$200 dentist
$440 copyright theft
$500 lawyer
$1000 copyright theft
$488 property manager
√$740.50 tax agency
$2,000 mortgage company
$2,500 realtor
$7,000 computer company
$x million condo association

These are some I haven't pursued beyond one letter because the time required is too much for too small a refund. But you can read the letters I wrote, so all is not lost (and some may eventually pay up):
$15.00 property manager
$12.50
handyman
$60.00 (former) friend
28.50 paid