Our clients often ask for splash pages, an intial graphic or animation that is played on a websites' home page.
Traditionally splash pages were disastrous from both a usablility perspective, users generally hate them - they want to get the information fast, and from a search engine perspective, at worst written in flash hiding the sites' content and at best presenting very little information on your homepage is a sure way not to get ranked highly.
My advice - don't have one - show the users a good intro to your websites'content and purpose together with clear navigation so that they can get to the information they are interested in fast. Of course if your website is built in HTML and correctly indexed by the search engines users can arrive at your site on any page so the splash page is pointless anyway.
That said there are some occassions when a splash page can be used, for creative companies they can present impact and sell their creative strengths, for me this can be done in others ways that dosen't compromise the usability of the website, but each to their own - if your client wants one give it to them!