corn syrup, sucrose
"The largest single additive used is sugar - around three percent of the total weight - masking the unpalatable taste of nicotine. Choosing a sweetened or flavoured cigarette brand allows smokers to inhale increased volumes of smoke, more easily absorbing the desired dose of nicotine. Over 80% of new smokers start below eighteen years of age - this is recognised by the industry and targeted in production and marketing strategies.[2]
"The use of sugars, honey, liquorice, cocoa, chocolate and other flavourings make cigarettes more palatable and 'aspirational' - particularly to children and the young."[1]When burned, sugar produces acetaldehyde, a chemical that interacts with the brain's neurotransmitters. Once the ability of acetaldehyde to increase the nicotine addiction was discovered, the sugar levels in cigarettes rose dramatically as tobacco companies took advantage of the new knowledge to hook younger smokers with good-tasting and highly-addictive cigarettes.
A good resource for more information on additives in cigarettes: http://www.ash.org.uk/?additives
[1] Action on Smoking and Health, Tobacco additives: cigarette engineering and nicotine addiction, July 1999. Section 4. - see: http://www.ash.org.uk/?additives
[2] Action on Smoking and Health, Tobacco Explained: the truth about the tobacco industry in its own words, June 1998. Chapter 3 - see http://www.ash.org.uk/papers/tobexpld3.html