Don’t go to every forum and post a topic that people can get them by mailing you.
Just donate them to http://isnoop.net/gmail/!
It is the second link in google when searching for gmail invites. (first is google itself)
If you want your invites to be used send your invites to them, as I did.
I got 50 invites to spare, quite a lot of work to send them all to them.
I’ve send about 150 to them, almost all now have been used.
Getting some emails to thank me for sending those invites is rewarding enough for me 🙂