Phlebotomy is a very short certificate program (less than one year) but is a skill also taught in several other programs that lead to a degree. Nurses and lab technicians (for example) learn the skill as part of their studies. Clinical Lab Technicians get an associates degree. Clinical Lab Technologists get a bachelor's degree (or higher) and specialized training.
X-ray Tech (Radiology Technician) is usually a 2 year Associate of Applied Science degree program though it can be an 18 month certificate program. A 4-year degree in the field (Diagnostic Imaging) includes more than just x-rays and goes into x-ray, sonograms, MRI, CT Scans, etc...
Sonogram Tech (Diagnostic Medical Sonography Technician) is an advanced certificate of about 1 year duration that (almost always) requires an associates degree and/or certification in a related field (radiology tech, nursing, orthopedic tech, etc...) before entry. Those programs that don't require an associates degree before entry must be two years (associate degree) programs to be accredited.
Information about each can be found in the Occupational Outlook Handbook:
Phlebotomist - in the entry on Clinical Lab Techs -
http://www.bls.gov/oco/ocos096.htm Radiology Technician -
http://www.bls.gov/oco/ocos105.htm Diagnostic Medical Sonographers -
http://www.bls.gov/oco/ocos273.htm Notice that generally here, the more training, the higher the payscale. A phlebotomist can expect to earn about $12 per hour whereas a sonographer can expect upwards of $30 per hour. Hospitals tend to need phlebotomists 24/7 (a lot of shift work) but most people don't get ultrasounds in the middle of the night, weekends, or holidays (though some do in emergencies). Phlebotomists (and other staff trained in the skill) will always be a need in every hospital coast-to-coast so it's a good certificate to have - it just doesn't pay as well as more advanced training.
Some health care HR people have noted that the need for "x-ray technicians" is falling rapidly with advances in imaging while the number of qualified imaging operators (CT, MRI, Nuc Med, Ultrasound...) isn't keeping up with the need for applicants. Note though that many RNs are adding diagnostic sonography to their credentials as more-and-more physician's offices add the equipment - it's hard to compete with the nurses for those jobs in offices.