Each weekday, TheStreet.com Ratings updates its ratings on the stocks it covers. The proprietary ratings model projects a stock's total return potential over a 12-month period, including both price appreciation and dividends. Buy, hold or sell ratings designate how the Ratings group expects these stocks to perform against a general benchmark of the equities market and interest rates.

While the ratings model is quantitative, it uses both subjective and objective elements. For instance, subjective elements include expected equities market returns, future interest rates, implied industry outlook and company earnings forecasts. Objective elements include volatility of past operating revenue, financial strength and company cash flows.

Investment bank

Goldman Sachs

(GS) - Get Report

has been upgraded to a buy from a sell. The company's revenue rose 49% in the third quarter compared with the same period last year, outpacing the industry average of 30%. Its EPS improved 88.03% in the same timeframe, continuing a two-year pattern of positive earnings growth.

On the back of its earnings success, Goldman Sachs' stock price has gone up by 31.80% in the last 12 months, and while almost any stock can fall in a broad market decline, it should continue to move higher despite the fact that it has already enjoyed a nice gain the past year. Although the company may harbor a few minor weaknesses, TheStreet.com Ratings believes they are unlikely to have a significant impact on results. Goldman Sachs had been rated a hold since August 2007.

Insurance, pensions, savings and investment products provider

Aegon

(AEG) - Get Report

has been upgraded to a buy from a hold. The company's revenue grew by 129.1% in the second quarter compared with the same period last year, exceeding the industry average of 13.2%. Its debt-to-equity ratio of 0.08 is below the industry average, implying that there has been very successful management of debt levels.

The company has reported somewhat volatile earnings recently, and EPS declined by 26.6% in the second quarter compared with the same period last year. Weak earnings growth has likely contributed to a fairly stagnant stock price, which has increased by 2.82% in the last 12 months. However, while even the best stocks can fall in an overall down market, in any other environment, this stock still has good upside potential. Aegon had been rated a hold since July 2007.

CPFL Energia

TheStreet Recommends

(CPL) - Get Report

, the Brazilian electric utility, has been upgraded to a buy from a hold. Its revenue increased by 37.6% in the second quarter compared with the same period last year, and net income improved by 45.8% to $206.64 million over that timeframe. Return on equity of 32.59% marked an improvement on ROE of 25.43% in the second quarter of 2006, a clear sign of strength within the company. Compared to other companies in the electric utilities industry and the overall market, CPFL's return on equity significantly exceeds that of both the industry average and the

S&P 500

.

Powered by EPS growth of 41.8% in the second quarter compared with last year, the company's stock has increased by 57.40% in the past 12 months, and should continue to move higher despite having enjoyed a nice gain in the past year. CPFL had been rated a hold since September 2007.

Real estate investment trust

Developers Diversified Realty Corporation

(DDR)

has been upgraded to a buy from a hold. Its revenue grew by 43.2% in the second quarter compared with the same period last year, and net income increased by 61.9% to $127.44 million in the same timeframe. The company's gross profit margin also increased, to 50%, and its net profit margin of 45.60% significantly outperformed against the industry average. Developers Diversified's return on equity of 6.64% improved over the year-ago quarter, which can be construed as modest strength in the organization. The company had been rated a hold since May 2006.

Virgin Media

(VMED)

, a provider of television, broadband, fixed-line telephone and mobile telephone services, has been downgraded to a sell from a hold. Despite a debt-to-equity ratio of 2.00, it is still below the industry average, which suggests that this level of debt is acceptable within the media industry. However, the company's quick ratio of 0.52 is low and demonstrates weak liquidity. Virgin's stock price has decreased by 2.48% in the past 12 months, and the fact that the stock is now selling for less than others in its industry in relation to its current earnings is not enough to justify a buy rating at this time. The company had been rated a hold since August 2007.

Additional ratings changes are listed below: