Social engineering with a touch of spoofing - often delivered by spam, IM, etc. and very remarkable when done. Do not be fooled - Check the URL. Usually there is something not quite right - Spelling, fonts, graphics. Vishing is done over the phone - Fake security checks or bank updates.
Phishing with inside information - makes the attached more believable, spear phishing the CEO is "whaling".
Use someone else to gain access to a building - not an accident.