Hi,
show ip bgp summary
will show you all BGP neighbors you are peering to.
You chose one you want to check which prefixes you are advertising to and use
sh ip bgp nei nei_ip_address adv
to list the prefixes you are advertising to that particular neighbor, as Edison said already.
Don't forget you might be advertising different sets of prefixes to different neighbors.
(read about bgp update-groups if you are interested).
HTH,
Milan
