Application notes, product tutorials, buying guides, from many test and measurement manufacturers
http://www.testmart.com/applicationnotes/appnotestmp.cfm
Application notes on the Z8 series Microcontrollers.
http://www.zilog.com/products/appnotes.asp
DataSheets. Choose transistors or diodes.
http://www.advancedsemiconductor.com/
Application notes and technical help.
http://www.maxim-ic.com/appnotes10.cfm/filter/category
Application notes, hierarchy listing
http://www.national.com/apnotes/
Nearly every manufacturer of any thing that could remotely be considered "electronics" is listed. Its easy to find the data sheets and applications notes from the links listed.
http://pw1.netcom.com/~dwsmith/list_numbers.html
From HP, Motorola and RS Microwave.
http://rf.rfglobalnet.com/library/DataSheets/home.htm
Application notes for chipsets and Direct RDRAM.
http://developer.intel.com/design/chipsets/applnots/