I wrote this for one of my smaller ports. Seems to work well enough for basic content management!

ContentCaseCheck.cs

/* ContentCaseCheck - XNA Content Case Sensitivity Verification Tool
 * Written by Ethan "flibitijibibo" Lee
 * http://www.flibitijibibo.com/
 *
 * Released under public domain.
 * No warranty implied; use at your own risk.
 */

using System;
using System.IO;

class ContentCaseCheck
{
	static void Main(string[] args)
	{
		/* Acquired with `find .` in Content/ folder */
		string[] files = File.ReadAllLines("file.txt");
		/* Acquired with some grep of Content.Load<T> in game source */
		string[] lines = File.ReadAllLines("list.txt");

		/* Trim out ./ from files list */
		for (int i = 1; i < files.Length; i += 1)
		{
			files[i] = files[i].Substring(2);
		}
		for (int i = 0; i < lines.Length; i += 1)
		{
			/* Trim out all text except for Content.Load param */
			string line = lines[i];
			int start = line.IndexOf('\"') + 1;
			int end = line.LastIndexOf('\"');
			lines[i] = lines[i].Substring(start, end - start);

			/* Check for the string in the file list */
			bool exists = false;
			foreach (string file in files)
			{
				if (file.Contains(lines[i]))
				{
					exists = true;
					break;
				}
			}
			if (!exists)
			{
				System.Console.WriteLine(lines[i]);
			}
		}
	}
}