Democracy as a whole or specific features of it? (Such as populism, parliamentarism, personality cults, etc?)
"Democracy" has many flavors ranging from kleptocracies to representative republics, each with its own specific set of dynamics to be evauated.
Also, are you looking for contemporary titles or classics?
For the latter, you might look to DeTocqueville and Edmund Burke.
For something contemporary, this might serve:
http://www.amazon.com/Life-Death-Dem.../dp/0393058352
Or, for a broader view:
http://www.amazon.com/Shield-Achille...hilles+bobbitt