Semiconductor manufacturers
---------------------------
www.analog.com - Analog Devices
www.ti.com - Texas Instruments
www.maxim-ic.com - Maxim
www.dalsemi.com - Dallas Semiconductor (now owned by Maxim)
www.burr-brown.com - Burr Brown (now owned by TI)
http://mot-sps.com - Motorola Semiconductors
http://www.onsemi.com - On Semiconductor
www.national.com - National (mostly analog stuff)
www.fairchildsemi.com - Fairchild (mostly digital stuff - used to be National)
www.linear.com - Linear Technologies

Distributors
------------
www.newark.com
www.insight-electronics.com
www.avnetmarshall.com
www.alliedelec.com

Mail-order
----------
www.digikey.com
www.jameco.com
www.jdr.com
www.mouser.com
www.allelectronics.com
www.mpja.com
www.cir.com
www.alltronics.com
www.unicornelectronics.com

If you need to find out who makes a chip from it's part number try:
http://www.embeddedlinks.com/chipdir/
You can search by the number or prefix on a chip.   They also have
pin-outs and links to most IC manufacturers.