The gift of money
According to The Complete Idiot's Guide to Etiquette
Babysitter or nanny: One week's pay plus a small gift

Trash collectors: $15–$20 each

Paper carrier: $15–$25 for daily delivery and $5–$15 for weekend delivery

Mail carrier: As federal employees, mail carriers can't accept more than $20, so $15–$20 is fine.

Doorman: $25–$120, depending on if he works with staff or alone.

Hairdresser: The equivalent of one session (or $25 if you're not a regular salon-goer)

If you're deciding between money and a present, it might help to know most people prefer the cash.