EODData – free EOD data for US equities and a few others
Google Finance – free EOD data for US equities
Yahoo Finance – free EOD data for US equities
Dukascopy – Free Historical Data Feed mainly FX
Finam – Russian site that offers free up to 1min intervals for different investment vehicles
Stooq – Free bulk download of many different equities around the world EOD or 1h or 5min
Wealth Lab Wiki – No idea, just came across and wanted to document in case I need it in the future
Data quality is important and I would not use any of these sources to build an extremely sophisticated strategy that e.g. aims to explore potential short term arbitrary opportunities… I am simply using them for my more general analysis and deal the results with care.