If you’re trying to make more people use the wiki, then that’s exactly what you need to do – I’m guessing you’re in a small team, so get one other person interested and get them to start putting information on the wiki. For example, do you have a list of projects plus a description of what they are, who is on them, their status and so on? That should be on the wiki.
Depending on your team and exactly what you do, maybe a “tips and tricks with PHP” page. Make it an internal point of reference for the rest of the developers and encourage them to add their own advice to everyone else.
The world’s your oyster in theory, but the content does need to be compelling in the first place to get people looking at it.
I do of course also maintain a fabulous list of wiki-related resources in del.icio.us which are well worth checking out