nmap -sT host - scanning with connect - FULLOPEN - basic scan - default for simple users
nmap -sS host - scanning with SYN packets - half open - default for root
nmap -sF host - scanning using FIN scan - managed to dDOS my box when i had silly LOG rules
nmap -sX host - scanning using XMAS scan 
nmap -sN host - scanning using null scan 
nmap -sU host - udp scan

nmap -sP host - finds out if box is up
nmap -sV host - returns services version for this OS
nmap -sT -O host - finds out OS version
nmap -sS -p 0-65535  host - scanning with SYN packets all ports

nmap -sP -v 192.168.1.* - explores the subnet around us

without -v it only shows hosts that are up
nmap -sP 192.168.1.*