SIP - Session Initiation Protocol - A protocol that is used to initiate the session and exchange call parameters, QoS etc., required to set-up the call. The packets are encapsulated using UDP transport layer protocol.
RTP - The media (audio/video) itself is carried by Real-time Transport Protocol. This can be considered as transport for VoIP packets. Not to be confused with UDP transport headers.
RTCP - RTP Control Protocol, also referred as Real-time Transport Control Protocol works together with RTP and is a control protocol to monitor the media (quality) in RTP session
RSVP - This comes in the context of QoS and is a Resource ReSerVation Protocol, a network control protocol that allows receiver to request a special treatment for data transmission.
RTSP - Can be considered a competitor to SIP. Real-time Streaming Protocol is yet another signalling protocol like SIP but more suited in client-server applications while SIP is primarily designed for peer-to-peer calling.
VoIP - It is an umbrella protocol that encompasses several different technologies to transmit Voice over Internet Protocol aka Voice over Internet/Network. SIP is one such technology.