One of the community-provided YQL tables looks like it will work for you: yahoo.finance.stocks.

Example YQL query: select CompanyName from yahoo.finance.stocks where symbol="TKR"

Update 2012-02-10: As firebush points out in the comments, this YQL community table (yahoo.finance.stocks) doesn t seem to be working correctly any more, probably because the HTML page structures on finance.yahoo.com have changed. This is a good example of the downside of any YQL tables that rely on HTML scraping rather than a true API. (Which for Yahoo Finance doesn t exist, unfortunately.)

It looks like the community table for Google Finance is still working, so this may be an alternative to try: select * from google.igoogle.stock where stock= TRK ;

I have screen scrapped this information in the past either using Yahoo Finance or MSN Money. For instance you can get this information for ExxonMobil by going to (link). As far as an API you might need to build one yourself. For an API checkout Xignite.

You can use the "Company Search" operation in the Company Fundamentals API here: http://www.mergent.com/servius/

You can use Yahoo s look up service using Jonathan Christian s .NET api that is available on NuGet under "Yahoo Stock Quotes".

https://github.com/jchristian/yahoo_stock_quotes

//Create the quote service
 var quote_service = new QuoteService();

//Get a quote
var quotes = quote_service.Quote("MSFT", "GOOG").Return(QuoteReturnParameter.Symbol,
                                                    QuoteReturnParameter.Name,
                                                    QuoteReturnParameter.LatestTradePrice,
                                                    QuoteReturnParameter.LatestTradeTime);

//Get info from the quotes
foreach (var quote in quotes)
{
    Console.WriteLine("{0} - {1} - {2} - {3}", quote.Symbol, quote.Name, quote.LatestTradePrice, quote.LatestTradeTime);
}

EDIT: After posting this I tried this exact code and it was not working for me so instead I used the Yahoo Finance Managed Api however it s not available via NuGet. A good example of use here

QuotesDownload dl = new QuotesDownload();
DownloadClient<QuotesResult> baseDl = dl;

QuotesDownloadSettings settings = dl.Settings;
settings.IDs = new string[] { "MSFT", "GOOG", "YHOO" };
settings.Properties = new QuoteProperty[] { QuoteProperty.Symbol,
                                        QuoteProperty.Name, 
                                        QuoteProperty.LastTradePriceOnly
                                      };            
SettingsBase baseSettings = baseDl.Settings;
Response<QuotesResult> resp = baseDl.Download();

Also if you just want to download the stuff stocktwits api has a download link for the symbology and industries under "Resources" http://stocktwits.com/developers/docs

It also possible to use Quandl.com resources. Their WIKI database contains 3339 major stocks and can be fetched via secwiki_tickers.csv file. For a plain file portfolio.lst storing the list of your tickers (stocks in US markets), e.g.:

AAPL
IBM
JNJ
MSFT
TXN

you can scan the .csv file for the name, e.g:

import pandas as pd

df = pd.read_csv( secwiki_tickers.csv )
dp = pd.read_csv( portfolio.lst ,names=[ pTicker ])

pTickers = dp.pTicker.values  # converts into a list

tmpTickers = []

for i in range(len(pTickers)):
    test = df[df.Ticker==pTickers[i]]
    if not (test.empty):
        print("%-10s%s" % (pTickers[i], list(test.Name.values)[0]))

what returns:

AAPL      Apple Inc.
IBM       International Business Machines Corporation
JNJ       Johnson & Johnson
MSFT      Microsoft Corporation
TXN       Texas Instruments Inc.

It is possible to combine more stocks from other Quandl s resources. See the documentation online.