Where do I install certificates so that wget and other MacPorts programs will find them?

The answer above didn't resolve the issue for me, but I found a similar easy solution with MacPorts:

sudo port install curl-ca-bundle

To install the Certificate Authrity bundle and then push its reference to the wget settings profile:

echo CA_CERTIFICATE=/opt/local/share/curl/curl-ca-bundle.crt >> ~/.wgetrc

Create a wgetrc file containing:

ca_directory=/System/Library/OpenSSL/certs

On Linux and BSD, the file is located at ~/.wgetrc (and /etc/wgetrc system-wide). I don't know if it is the same for MacPorts.

I can't add a comment to grawity's solution, so I guess I'll create a new answer...

grawity's solution seems to be incomplete. It worked because you had already "tried installing in /System/Library/OpenSSL/certs".

I installed OpenSSL from MacPorts (newer than the version included with my Snow Leopard install). This put a cert.pem file in /opt/local/etc/openssl/, which I could then point to with grawity's method. This is essentially what I did:

sudo port install openssl
sudo echo 'ca_directory = /opt/local/etc/openssl' > /opt/local/etc/wgetrc
sudo cat /opt/local/etc/wgetrc.sample >> /opt/local/etc/wgetrc`

Ain's solution probably would have worked for me as well.