I did some searching on this forum and on the web but I keep getting conflicting information on this topic.

What is the best (i.e. easiest to set-up and most secure) "Donate Now" button that a webmaster can put on his site. Just a simple text field for a user to add their Bitcoin Address for sending the payment and a one-click button that would send a predetermined amount to a fixed Bitcoin Address owned by the web site?

So far it looks like blockchain.info has an API for doing this - are there others? Are there community built or open source projects that do the same?

Another question if you don't mind. If BTC transactions can not be reversed, what stops someone from putting a "Donate 0.0001 BTC" button that actually sends 1 BTC to the destination? I feel like I'm missing something integral here....

Thanks all for your wisdom!