This page offers fully interactive previews of my QR code generators. They are entirely free and open source and do all the work in your browser. This means the text you type will not be sent to a remote server. It also enables you to download them and use them on a computer not connected to the internet. You can click the link above a preview to jump to the corresponding website.
This QR code generator offers some convenience features such as being able to drag & drop (or copy-paste) a file into the textbox. If the browser supports it (and you allow it), it can also constantly monitor the systems clipboard and generate a QR code from the clipboard's contents. (Download)
This QR code generator is designed to be as small as possible and thus offers significantly fewer features. (Download)