A lot of people who do use Bitcoin on their website, blog or what ever it may be just post their address for donations. Payment gateways do exist such as bitpay which are commonly used for selling goods for Bitcoin and possibly even services too.
In the nature of wordpress I don't think a highly sophisticated system needs to be used and posting your Bitcoin address it probably good enough. We don't always have to over complicate things for them to be good.
My only concern about posting the bitcoin address on a website is that from the moment you post your address waiting for donations, everyone will be able to check how much donations you have received so far...
Somewhere I have read about a kind of script that periodically changes the address displayed on the website to oversome this privacy problem.
