Monday's Analysts' Upgrades, Downgrades

Change in Ratings

Aspen Insurance(AHL Quote) 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 Quote) 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 Quote) initiated at UBS with buy rating. Price target starts at $37 and fiscal year 2008 EPS estimates begin at $2.05.

Dollar Tree(DLTR Quote) upgraded at JPMorgan to neutral from underweight. Most of the negative catalysts have played out since the CFO left last October.

DRS Technologies(DRS Quote) 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 Quote) upgraded at JPMorgan from neutral to overweight. Valuation call, especially as fundamentals improved in the first quarter.

Imclone(IMCL Quote) 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 Quote) 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 Quote) 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.