The Numbers

Ethernet
1518 Maximum Ethernet frame length in bytes
64 Minimum Ethernet frame length in bytes
14 Ethernet header length in bytes
46 Minimum Ethernet data length in bytes
1500 Maximum Ethernet data length in bytes
4 Ethernet trailer length in bytes
8 Ethernet Preamble length in bytes (inc. SoF Delimiter)
12 Interframe Gap in bytes

802.1Q
1522 Maximum Ethernet frame length w/ 802.1Q tagging
18 Ethernet header w/ 802.1Q tagging
4 802.1Q tag length in bytes

IP
20 Minimum IP header length in bytes

TCP
20 Minimum TCP header length in bytes

GRE
4 Minimum GRE header length in bytes
1476 GRE MTU in bytes, assuming 1500 Ethernet MTU
1436 GRE encapsulated TCP MSS in bytes

Sources:
http://en.wikipedia.org/wiki/Ethernet
http://sd.wareonearth.com/~phil/net/overhead/
http://www.ethermanage.com/ethernet/ethernet.html