No matter the market, there will always be losers -- a few lagging disappointments holding back a Wall Street rally, or several big losers leading a bearish day. The S&P 500 (SNPINDEX:^GSPC) had a historic day, picking up more than 1%, and crossing the vaunted 1,600 mark. Yet, even with all the optimism on Wall Street today, several notable names held back the index from even greater gains, and made investors pull their hair out in frustration. Here are the three worst stocks today that you need to know about -- from utilities to computer systems, these stocks put a dent in Wall Street's Friday.

No gains from these stocks
Unsurprisingly, earnings drove today's big losers down on a day where most stocks rose. Exelon (NYSE:EXC) reported earnings back on Wednesday, and while the company managed to beat analyst expectations on both its top and bottom lines, Exelon's $4 million quarterly loss was enough to send investors fleeing. The stock fell nearly 1.5% today, and shed 4.3% this week, despite a 21.8% year-to-date run-up. Higher costs and tightening margin  are threatening the stock's finances, and while the company hopes to boost margins by 2015 by closing old coal plants, cheap natural gas will likely continue to press on Exelon's profit in the near future.

Computer systems and warehousing firm Teradata (NYSE:TDC) was another victim of earnings today, dumping more than 4.5% after a disappointing quarterly report. The company's earnings fell 35% year over year, and revenue fell 4%, with both figures missing analyst expectations. Teradata leadership still expects growth this year, but with companies tightening their IT budgets, and CEO Mike Koehler's admission of "softness in large capital purchases," the firm could be under pressure throughout the near future.

Neither of these firms' falls was even close to the losses experienced by today's big loser, however. Today's top laggard comes from outside the S&P 500, as LinkedIn (NYSE:LNKD) shares fell nearly 13% during the trading day after -- surprise -- it released earnings. The company's profit and revenue both topped analyst projections for the prior quarter, but it was LinkedIn's outlook that sparked investor panic.

The company projected second-quarter revenue at a range between 4% to 5% lower than what analysts had projected, alongside full-year expectations that similarly missed the mark. Some analysts have voiced concerns that the company's shift to mobile advertising hasn't gone as smoothly as planned, and although LinkedIn's membership has almost doubled since its IPO, the firm's more than 225 million members leave questionable room for future growth. Despite the downbeat outlook, the firm's shares have jumped an astronomical 79% this year, and investors who have held the stock for some time have yet to feel anything close to losses set in.

The future of power?

Fool contributor Dan Carroll has no position in any stocks mentioned. The Motley Fool recommends Exelon, LinkedIn, and Teradata. The Motley Fool owns shares of LinkedIn. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.