The simplest way in my opinion is simple - underline the link!
Since older days when links were invented, they were all underlined and easy to recognise. Underlining was the simplest, most obvious, unambiguous way of displaying links.
Then this new trend came in and, for some reason, sites started removing the underlines. Maybe because they were perceived "boring", "old-fashioned", "ugly", whatever. Unfortunately, the result is the constant confusion battling the user to guess whether this or that is still a link or not. And then, even worse, underlining became used for other purposes than links. To have the confusion reach its perfection :)
So my advice is simple:
If the purpose of your site is to impress the user with unique beauty and style, e.g. if you are web designer looking for job, by all means use your creativity and originality.
If, on the other hand, your site's purpose is practical and functional, and, most important, is meant to be simple to use, please put the UX and usability before the beauty, and underline your links. And don't underline anything else.
Sites like amazon or ebay are not beautiful but they work.