American International (AIG) had the best month in 2009 by a large-cap US stock in August 2009, returning 241.1%.

ASSET	MONTH	% RETURN
American International (AIG)	August 2009	241.08%
Celsius (CELH)	March 2009	180.02%
EXACT Sciences (EXAS)	January 2009	161.4%
Las Vegas Sands (LVS)	April 2009	145.91%
Ford Motor (F)	April 2009	133.59%
Celsius (CELH)	July 2009	129.89%
Primo Brands (PRMB)	May 2009	112.27%
Pilgrims Pride (PPC)	April 2009	110.51%
Insmed (INSM)	February 2009	109.09%
Principal Financial (PFG)	April 2009	106.31%
Pilgrims Pride (PPC)	March 2009	104.55%
Owens Corning (OC)	April 2009	101.35%
Tenet Healthcare (THC)	April 2009	99.12%
Freedom (FRHC)	May 2009	97.5%
Wynn Resorts (WYNN)	April 2009	96.15%
Teck Resources Ltd Class B (TECK)	April 2009	95.55%
Dupont De Nemours (DD)	April 2009	93.47%
American International (AIG)	March 2009	92.31%
CBRE Group Inc Class A (CBRE)	April 2009	91.33%
Textron (TXT)	April 2009	90.25%
Bank of America (BAC)	March 2009	89.44%
American Express (AXP)	April 2009	89.06%
Barclays PLC ADR (BCS)	April 2009	88.79%
Primo Brands (PRMB)	April 2009	88.79%
Royal Caribbean Cruises (RCL)	April 2009	88.6%

Large-cap stocks are treated as having a market cap of $10B+.