If you didn't want to sign up for a service, I'd probably go back to the exchanges themselves; most of them aren't CAPTCHAed yet...
The symbol lookup page for:
- NYSE is at http://www.nyse.com/interface/html/SymbolLookup.html
- NASDAQ is at http://www.nasdaq.com/asp/NasdaqSymLookup2.asp?mode=stock
- London Stock Exchange is at http://www.londonstockexchange.com/en-gb/pricesnews/prices/Trigger/genericsearch.htm
- ASX is at http://www.asx.com.au/asx/research/codeLookup.do
etc...
