ASA 5505, is BGP supported?

I see that this question was asked in April 2010. Good news is that four years later (April 2014) Cisco released ASA software version 9.2(x) with new BGP support! See the ASA 9.2(x) release notes for details. If you're using the ASA 5505, you should review the 5505 RAM requirements listed in the release notes.

ASA users have been asking for this feature for a long time - it's good to finally see it delivered :-).

ASA doesn't support BGP whatever the model.
This information is in the documentation, see http://www.cisco.com/en/US/docs/security/asa/asa80/configuration/guide/glossary.html#wp1027964

Update

BGP is supported on ASA from v9.2 (release notes).

Configuration examples are available. The keywords are similar to IOS.

router bgp 100
 bgp log-neighbor-changes
 bgp bestpath compare-routerid
 address-family ipv4 unicast
  neighbor 203.0.113.2 remote-as 200
  neighbor 203.0.113.2 activate
  network 192.168.10.0 mask 255.255.255.0
  network 172.16.20.0 mask 255.255.255.0
  network 10.106.44.0 mask 255.255.255.0
  no auto-summary
  no synchronization
 exit-address-family
!