Getting invited onto Google Wave can be a challenging task. Web site Google Wave Invites offers a more organised alternative.
By nature of the way Google is handing out Wave invites, it's difficult to know with any amount of certainty that someone has sent you an invite because Google isn't instantly sending invitations to people you invite. Instead, they're going through them one at a time—meaning that the Lifehacker editors who I invited as soon as I got access, for example, still haven't received their invitations.
One adventurous, helpful web developer put together a web site dedicated specifically to the giving away and receiving of Google Wave invites—called Google Wave Invites—and it seems worth a try if you're looking for an invite. If you have been enjoying the spoils of Wave, let's hear how you've liked using it so far in the comments.