Aspen Insurance ( AHL) upgraded at Goldman Sachs to buy from neutral based on valuation. See attractive risk/reward profile with shares trading at 0.87 times last reported book value. American International Group ( AIG) downgraded at Goldman to neutral from buy based on balance sheet pressures and dilutive capital raises. See lower investment income and higher general insurance accident-loss ratios. Price target cut to $45 from $59. Commercial Metals ( CMC) initiated at UBS with buy rating. Price target starts at $37 and fiscal year 2008 EPS estimates begin at $2.05. Dollar Tree ( DLTR) upgraded at JPMorgan to neutral from underweight. Most of the negative catalysts have played out since the CFO left last October. DRS Technologies ( DRS) downgraded at Credit Suisse from outperform to neutral with a $73.50 price target. Rumored acquisition by Finmeccanica more than 50% likely to happen, but the potential price remains unclear. El Paso ( EP) upgraded at JPMorgan from neutral to overweight. Valuation call, especially as fundamentals improved in the first quarter. Imclone ( IMCL) downgraded at Morgan Stanley from equal-weight to underweight with a $38 price target. Do not expect ASCO data to meet expectations. Erbitux sales estimates also cut. Markel ( MKL) downgraded at Goldman Sachs to sell from neutral based on view that shares will underperform peers as investors flock to beaten down names with lower multiples. Marsh & McLennan ( MMC) upgraded at Goldman Sachs to neutral from sell based on improving sentiment towards turnaround efforts. Note investors are giving management the benefit of the doubt.