802.11b - 11 Mbps (2.4GHz)
802.11a - 54 Mbps (5 GHz)
802.11g - 54 Mbps (2.4GHz)
802.11n - 600 Mbps (2.4GHz and 5 GHz) - 150Mbps typical for network adapters, 300Mbps, 450Mbps, and 600Mbps speeds when bonding channels with some routers
802.11ac - 1300+Mbps (5 GHz) - newer standard that uses wider channels, QAM and spatial streams for higher throughput
Actual wireless speeds vary significantly from the above theoretical maximum speeds due to:
distance - distance from the access point, as well as any physical obstructions, such as walls, signal-blocking or reflecting materials affect signal propagation and reduce speed
interference - other wireless networks and devices in the same frequency in the same area affect performance
shared bandwidth - available bandwidth is shared between all users on the same wireless network.
1@DaveM I rolled back your edit. Those weren't spelling errors, "2.4G" and "5G" is how wireless routers are marketed. – Indrek – 2013-01-25T13:57:49.600
@Indrek Have not seen that in manufacturers info. Have seen 802.11AC refered to as 5G in some material. – Dave M – 2013-01-25T14:11:40.870
@DaveM Wild guess, but could 5G in that context mean "generation 5" (after a, b, g and n)? Anyway, plenty of dual-band, non-ac routers are marketed as 2.4G+5G. Example: http://www.amazon.com/SANOXY-Concurrent-300Mbps-Wireless-integrated/dp/B005NXS3FI
– Indrek – 2013-01-25T14:18:25.303