Below is the list the TSA post on their www site. It's a PDF file. Also included is the FAA's list.

http://www.tsa.gov/interweb/assetlib...12_18_2003.pdf

http://asi.faa.gov/these.asp

More to the question of the helium balloon, this is a question that can be asked of a UA employee. They have access to a profile as well as other resources which their company provides.

If you should have concerns about what you might think is a dangerous good or hazardous material, please feel free to contact either one of the resources I have listed.