AIRLINES

Hawaiian Airlines (receipient must have credit card holders only)
British Airways (through household accounts; several restrictions apply please research before going into this)
Qantas (once a year)
Korean (family pooling)
Emirates (earning miles in one account at reduced rate)
Qatar (same as EK)
Sun Country Airlines.
Kuwait Airways (same as EK)
Virgin Australia (family pooling)

HOTELS

Starwood (online; for those at the same address)
Marriott (not online; only when redeeming awards)
Club Carlson (not online)
Hyatt (not online; only when booking reward nights)

CAR RENTALS

Hertz (via phone; one family member to another if both are gold)


CREDIT CARDS

Chase UR (online; to spouse's FFP or UR need receipient's credit card # to transfer to other's UR)
Amex MR (transfers to other's MR account by special email request; transfers to others FFP online)
Capital One (transfers to other's Capital One credit card)
Citi Thank You (online transfers to others TYP account; need TYP# or credit card/checking account #, transfered points expire in 90 days)

Anything else?