You can get above C by disabling SSLv3 and maybe above B if you fix the ciphers, and other than that you just have to make a new cert signed with SHA2. Actually the intermediate cert is weak too so I dunno. Maybe a different CA. StartSSL is good. Free.
Here's my config (nginx) that gets me A+ (along with a strong cert):
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;