Resources

http://cchs-dl.slis.ua.edu/patientinfo/alcohol/caffeine.htm
http://www.wisegeek.com/what-is-caffeine.htm
http://www.mayoclinic.com/health/blood-pressure/AN00792
http://www.faqs.org/nutrition/Ca-De/Caffeine.html
http://www.cyh.com/HealthTopics/HealthTopicDetails.aspx?p=243&np=163&id=2155

Sources of caffeine

The richest sources of caffeine are tea, coffee, cola drinks, some over-the-counter medications, chocolate, and cocoa.
As little as 20 mgs of caffeine can produce noticeable body and mood changes. As a very rough guide to how much caffeine you may be taking on a daily basis...
An average cup of tea contains around 50 mgs of caffeine.
An average cup of instant coffee contains around 70-100 mgs. Instant decaffeinated coffee contains about 3 mgs.
A 6 oz cup of espresso coffee (much larger than the normal cafe cup, incidentally) contains about 80-90 mgs. A single-hit cappuccino will contain the same amount.
Filter coffee (called 'drip' in the US) can contain 25-50% more caffeine than instant.
A 340 ml or 12 oz can of regular or diet cola contains between 35 and 45 mgs. of caffeine depending on the brand
One ounce or 28 grams of chocolate contains about 10-15 mgs .
(An average cup is about 6 UK fluid ounces or 170 ml. Your precise intake of caffeine will, of course, vary with the strength of the drink. One person's mug of instant coffee might have 75 mgs while another person might prepare a 200 mgs hit! Useful link: CoffeeFAQ)