I have seen a couple of wordpress plugins which you can find easily with a search. I have never used any of them since I never felt the need.

you are not asking for payment to want to generate a new address each time so your job is super easy. you just have to show them your address (bitcoin or anything else). and for that simply put up your QR code which you can create using any tool online (string to QR thing) or simply go to one of the block explorers like blockchain.info and save the QR image it shows on your address page.

you can also use bitcoin URI scheme or BIP21 to place a clickable link on your website so that users can automatically open their wallets by clicking on it. like this:
testing BIP21 link
read the details here: https://github.com/bitcoin/bips/blob/master/bip-0021.mediawiki