* Euro zone finance ministers in third attempt at Greek deal
* Investors take profits after last week's strong finish
* Knight Capital in talks for unit sale; shares jump
* Indexes off: Dow 0.6 pct; S&P 0.5 pct; Nasdaq flat
By Rodrigo Campos
NEW YORK, Nov 26 (Reuters) - U.S. stocks slipped on Monday after Wall Street posted its best week in over five months as investors reacted to a lack of visible progress in budget deficit discussions in Washington.
The S&P 500 was holding above the 1,400 level it retook last week, and volume continued to be weak as traders awaited any advance in talks over a series of spending cuts and tax hikes scheduled to begin next year, which threaten to drag the economy into recession.
Retailer shares fell, with the S&P 500 retail index off 0.7 percent after the start of the holiday shopping season over the four-day Thanksgiving weekend.
"The concern is big retailers are discounting so much, sales look better, but at what cost?" said Angel Mata, managing director of listed equity trading at Stifel Nicolaus Capital Markets in Baltimore.
Bucking the trend, shares of eBay hit their highest in almost eight years with a 4.6 percent jump to $51.27 on strong sales data for Monday. Amazon gained 1.1 percent to $242.45. Black Friday sales online topped $1 billion for the first time.
Meanwhile, U.S. lawmakers have made little progress toward a compromise to avoid the "fiscal cliff," according to a top Senate Democrat who was interviewed over the weekend.
Indications of progress in talks, or just political willingness to negotiate, were part of the reason why the market rallied last week.
In the other major worry for the market, euro zone finance ministers and the International Monetary Fund made their third attempt in as many weeks to agree on releasing emergency aid for Greece, with policymakers saying a write-down of Greek debt is off the table for now.
"We had a good week last week and absent any news we were going to give something back today," Mata said. "There's no catalyst to continue the rally we saw last week, though Greece would have been important if we weren't dealing with the fiscal cliff."
The Dow Jones industrial average fell 77.92 points, or 0.60 percent, to 12,931.76. The S&P 500 Index dropped 6.99 points, or 0.50 percent, to 1,402.16. The Nasdaq Composite Index shed less than a point at 2,966.75.
Major indexes ended last week with gains of 3 to 4 percent, with the Dow above 13,000 and the S&P above 1,400 for the first time since Nov. 6.
Shares of Knight Capital Group Inc jumped 17.7 percent to $2.93 following reports that rivals might be preparing to bid for part or all of the electronic trading firm.
Apple Inc has asked a federal court to add six more products to its patent infringement lawsuit against Samsung Electronics, including the Samsung Galaxy Note II, in the latest move in an ongoing legal war between the two companies. Apple shares were up 2.8 percent at $587.37.