Replication options in Postgres

I am setting up a system that processes transactions, and it needs to
be highly reliable.  Once a transaction happens, it can never be
lost.  This means that there needs to be real-time off-site
replication of data.  I'm wondering what's the best way to do this.

One thing that might simplify this system is that I _never_ use UPDATE
or DELETE.  The only thing I ever do with the database is INSERT.  So
this might make replication a little easier.

I think I have a few possibilities:

1. In my PHP code, I have functions like
inserttransaction(values...).  I could just modify inserttransaction()
so that it runs the same query (the INSERT) on two or more DB
servers.  This would probably work ok.

2. I could write triggers for all my tables, so that when there is an
INSERT, the trigger does the same INSERT on the other server.  Any
ideas for an efficient way to do this?

3. Any other tricks?

I don't need mirroring.  There will be one master and one or more
slaves, and the only thing the slaves will do is store backup data.
The most important thing is that I can't lose a single transaction.

Thanks,

e