2005 filing (only one have looked at so far) mentioned Goldman Sachs quite a few times (about halfway into the link below it starts). Under realized gains/loses there is also Pfizer, Viacom, Freddie Mac, Chevron, and others.
Not sure if it amounts to much (tis late and just glanced this one over) but thought I would toss it out there for others to make sense of.
http://romneyfacts.com/assets/cjtk-life/life-charitable%20activity/tyler%20charitable%20foundation%2099/2005-form%20990-tyler%20charit.pdf
Charitable activity:
IRS Form 990s disclosure filings for donations made by The Tyler Charitable Foundation (formerly known as the Ann D & Mitt Romney Charitable Foundation II), and other key financial data.
tyler 1999
tyler 2000
tyler 2001
tyler 2002
tyler 2003
tyler 2004
tyler 2005
http://romneyfacts.com/cjtk.php