The International Congress of Mathematicians is being held 22-30 August, 2006, in Madrid. It is the pre-eminent mathematical congress, and is put on every two years. Here’s a link: http://www.icm2006.org/
I’m planning on going to give a short talk on my thesis work and extensions to it – I’ll pay for it out of my own pocket and annual leave if work isn’t willing to. Lucky academics – they often get funding to go to conferences as its part of their job!