From Wikipedia: Client configuration parameters.

A DHCP server can provide optional configuration parameters to the client. RFC 2132 defines the available DHCP options. RFC 1497 lists Vendor Extensions.

Some options worth committing to memory are:

67 = Bootfile-Name
72 = www-server (option 72 ip 1.1.1.1 2.2.2.2 3.3.3.3)

132 = 802.1P VLAN ID
133 = 802.1Q L2 Priority

120 = SIP Servers DHCP Option
128 = TFTP Server IP address (for IP Phone software load)
150 = TFTP Server IP address (Used by Cisco phones / CCM)

Wikipedia has actually categorised the options which is very nice and makes the list more comprehensible.

Less commonly known but still good to know for one of those ‘weird’ lab questions:

no ip dhcp snooping information option

The 3750 inserts a DHCP information option in the Discover request by default.  Some DHCP servers (like Microsoft) will drop such a DHCP Discover.