Options:
{{{
[Link]
[[Link]]
[Link|Text]
[Text|Link]
[[Link|Text]]
[[Text|Link]]
}}}

Almost all wikis use square brackets ({{{[[]]}}}) to make links. Using double square brackets allows single square brackets to be used freely without worry of turning them into links.

Using the same markup for both internal and external links makes it easier to learn and remember.

{{{[[Link|Description]]}}} was chosen since most wikis put the link before the text and this is also a precedence of HTML.

Raw URLs included in text are distinctive enough to be detected easily. Making them into links saves the users some hassle.