Most of them. It would help if you say what you want. Just go online and it's usually not hard to select "Sample" and see if it comes free or if it comes with a price. They do limit how many you can get from them, often totaling what you've gotten from them over the last 3 months or so.
i agree that sometimes finding the samples link is somewhat time consuming and at times it looks as if the manufacturer doesnt give samples at all. just do a little surfing around. and by luck u will find the samples link. but on sites like TI, maxim, microchip and the like, u can go to the samples page very easily.