1a) staff, family, couple, etc. -- variable: singular in reference to the whole (The staff is very large), plural in reference to the members (The staff wear casual clothes on Fridays)
1b) committee, board, jury, etc. -- also somewhat variable, but more often plural in BE than AE
2a) company, firm, society, club, etc. -- always singular in AE, often plural in BE in reference to the leaders/decision makers
2b) sports team, musical ensemble, etc. -- always singular in AE, usually plural in BE in reference to the players
3) police -- always plural in English (AE/BE)
This is just off the top of my head; especially the a) vs. b) groups are a bit hard to pin down, as usage can vary from person to person and case to case. For a better list, check an advanced grammar book or an online ESL/EFL site.
See also
related discussion:police is/are -- Polizei related discussion:Your class are planning a trip to Nottingham.related discussionand many others. For more, use the search engine of your choice + 'site:.leo.org.'