There is a CitiBank mobile site @ online.citibank.com. However, when I try to connect from either the built in browser or Dolphin I get a security warning that the certificate for the site is not valid. Viewing the certificate shows that it expires on 12/31/1999. Called CitiBank support but they were not too much help.
If you ignore the certificate warning and proceed to CB, you can access their mobile web page. The good news for Bank of America users is that they already have a great app for Droid. Now if my wife will just drop the CB account...