Alternatively, don't allow your users to put the tags in in the first place! This makes it easier to protect yourself and your users against craziness involving some of the other attributes of the <a> tag, like target, onclick and so on.
In reply to Re: How to recognize url in text and convert to hyperlink, unless already in anchor
in thread How to recognize url in text and convert to hyperlink, unless already in anchor by Anonymous Monk
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>