I needed a quick file caching solution and here is what I came up with …

    using System;
    using System.Collections.Generic;
    using System.IO;
    using System.Text;

    /// <summary>
    /// Provides a file model used by the <see cref="FileCache"/> type.
    /// </summary>
    public class FileModel
    {
        /// <summary>
        /// Gets or sets information about the file.
        /// </summary>
        public FileInfo Info { get; set; }

        /// <summary>
        /// Gets or sets the last time that the file had it's contents cached.
        /// </summary>
        public DateTime LastUpdate { get; set; }

        /// <summary>
        /// Gets or sets the file content for the file.
        /// </summary>
        public StringBuilder  Data { get; set; }
    }

    /// <summary>
    /// Provides a caching for file content based on file extensions.
    /// </summary>
    public class FileCache
    {
        /// <summary>
        /// Holds a singleton instance of a <see cref="FileCache"/> type.
        /// </summary>
        private static FileCache singleton;

        /// <summary>
        /// Used to hold the contents of the files.
        /// </summary>
        private readonly Dictionary<string, FileModel> files;

        /// <summary>
        /// Holds the list of extensions for files that will have there contents cached.
        /// </summary>
        private readonly List<string> extensions;

        /// <summary>
        /// Gets or sets a time value used to determine if a files content should be read again.
        /// </summary>
        public TimeSpan CacheTime { get; set; }

        /// <summary>
        /// Gets a list of file extension that will have there contents cached.
        /// </summary>
        public List<string> Extensions
        {
            get
            {
                return this.extensions;
            }
        }

        /// <summary>
        /// Default constructor.
        /// </summary>
        public FileCache()
        {
            this.files = new Dictionary<string, FileModel>();
            this.extensions = new List<string>();
            this.extensions.AddRange(new[] { ".htm" });
            this.CacheTime = TimeSpan.FromSeconds(2);
        }

        /// <summary>
        /// Provides a helper method for retrieving a file.
        /// </summary>
        /// <param name="path">The path to the file.</param>
        /// <returns>Returns a <see cref="FileModel"/> type containing information about the file.</returns>
        public static FileModel GetFile(string path)
        {
            return Instance.Get(path);
        }

        /// <summary>
        /// Provides a helper method for retrieving a file.
        /// </summary>
        /// <param name="path">The path to the file.</param>
        /// <returns>Returns a <see cref="FileModel"/> type containing information about the file.</returns>
        public FileModel Get(string path)
        {
            // if file does not exit just return null
            if (!File.Exists(path))
            {
                return null;
            }

            // check if file already exists in the cache
            FileModel model;
            if (this.files.ContainsKey(path))
            {
                // get existing entry
                model = this.files[path];
            }
            else
            {
                // add new entry
                model = new FileModel { LastUpdate = DateTime.Now, Info = new FileInfo(path) };
                this.files.Add(path, model);
            }

            // check to cache file data
            if (this.extensions.Contains(model.Info.Extension))
            {
                // not data has been read yet OR (the current time has surpassed the last update time plus the cache time AND 
                // the current time is greater then the last write time  ) we can read the contents of the file
                if (model.Data == null || (DateTime.Now > model.LastUpdate + this.CacheTime && DateTime.Now > model.Info.LastWriteTime))
                {
                    model.Data = new StringBuilder(File.ReadAllText(model.Info.FullName));
                }
            }

            // return the modal data
            return model;
        }

        /// <summary>
        /// Gets a singleton instance of a <see cref="FileCache"/> type.
        /// </summary>
        public static FileCache Instance
        {
            get
            {
                return singleton ?? (singleton = new FileCache());
            }
        }
    }