I am experimenting building an in-house Bitcoin payment system. 

What is currently the recommended practice to get notifications to your web server when a certain Bitcoin address receives a transaction? E.g. trigger an action from somewhere which results a HTTP call made to a web server.

Are there any better alternatives than polling bitcoind? 

External systems (blockchain.info) are good to go too for me.

Any way to filter for certain confirmation threshold (e.g. need 6 confirmations)?