Brad Abrams blogged a list of web hosters offering ASP.NET AJAX (formerly "Atlas"), including one in France, and a slew of write-in hosters are included in the comments of his post.

You definitely want a hoster that supports ASP.NET AJAX. Even if all you use is the UpdatePanel control for partial page updates.

Hosters: Are any of you offering ASP.NET AJAX in Ireland yet?