How to announce a new web-page?
If there's a reason for someone to visit your lab's site other than it's new and should be visited, then you could write up a short announcement and post it to a relevant mailing list for your particular discipline or sub-discipline.

Otherwise, the best and most persistent advertising you and your groupmates can do would be to include it as a signature block in your email. People who want to know more about your group can then click on the link. Other methods to generate traffic without purpose will likely tick off more people than inspire them to visit your page.