I attended the @media 2005 conference last year (obviously!). It was by far the best and most useful conference I have ever been to. The speakers included some of the best known names in the industry. Every single presentation was excellent. And the evenings were a great opportunity to meet other professionals.
Vivabit are doing it again this year with @media 2006, this time in a much larger venue. I just registered for it so I will definitely be there. If you are involved in web design, you should book 15th and 16th of June in your calendar, register for @media 2006 and arrange travel to London now. Your boss might need a bit of persuasion to pay for it but believe me: this will be an investment that will pay for itself several times over.