High availability in postgresql
This is pretty broad. Let's answer (2) first:

http://www.postgresql.org/support/professional_support/

Now, on to (1):


  Is there any good conceptual design that could offer reliable pgsql
  cluster - reliability, data corruption prevention, high availability,
  no SPOF, load balancing and access to DB through one (virtual?) IP
  address?


The question is not "if" but "which".

You are describing a heartbeat/failover cluster. There aren't really fully canned solutions for this, you'll need your own heartbeat and STONITH using appropriate non-PostgreSQL-specific tools.

You can use PostgreSQL 9.1 streaming replication and log shipping for the replication. The replication manager repmgr can help automate much of the management.

Other replication options are described on the PostgreSQL wiki. All will require added heartbeat and STONITH for a fully transparent cluster with virtual IP, etc.

You might also want to look at pgbouncer. It's a useful tool not only for connection pooling, but also for failover and load balancing.

See the PostgreSQL manual on high availability, load balancing, and replication for more information.