Well, I managed to miss this when it happened but thankfully it is an on-going deal. As part of their Veteran's Day 2011 offers, Sam's Club is now offering a $15 gift certificate to military folks who purchase a Sam's Club membership. The membership may be either the $40 Advantage membership or the $100 Advantage Plus membership.
This special offer is available to active duty or retired military personnel or their spouses, plus civilian military employees and their spouses. It does not define "civilian military employees" in the press release.
I always do a lot of math before purchasing a warehouse club membership. This extra $15 could make the math work out differently if you are unsure if you would benefit from a warehouse club membership. And if you already join Sam's, this is a great bonus next time you renew your membership.