SharpVPK:

A memory-friendly and fast parser for Valve's VPK files created in C#

Outputting the name of all entries to console:

var archive = new VpkArchive();
archive.Load(@"vpk_file_path.vpk");

foreach(var directory in archive.Directories)
	foreach (var entry in directory.Entries)
		Console.WriteLine(entry.ToString());

Console.WriteLine("Done");
Console.ReadLine();

which will return something similar to

Writing all files to a directory:

var archive = new VpkArchive();
archive.Load(@"vpk_file_path.vpk");

foreach(var directory in archive.Directories)
	foreach (var entry in directory.Entries)
		File.WriteAllBytes(@"C:\Output\" + entry.Filename + "." + entry.Extension,
			entry.Data);

Console.WriteLine("Done");
Console.ReadLine();