System.IO.Path. Its there, so use it!
It seems to me that one of the most underused, but very useful classes is the System.IO.Path class. It has a bunch of static methods which are extremely valueable when dealing with file system paths. Use it instead of doing some string parsing hack jobs!
Here is a list of methods:
ChangeExtension : Changes the extension of a path string.
***Combine : Combines two path strings.
***GetDirectoryName : Returns the directory information for the specified path string.
GetExtension : Returns the extension of the specified path string.
***GetFileName : Returns the file name and extension of the specified path string.
GetFileNameWithoutExtension : Returns the file name of the specified path string without the extension.
GetFullPath : Returns the absolute path for the specified path string.
GetPathRoot : Gets the root directory information of the specified path.
***GetTempFileName : Returns a uniquely named zero-byte temporary file on disk and returns the full path to that file.
GetTempPath : Returns the path of the current system's temporary folder.
HasExtension : Determines whether a path includes a file name extension.
IsPathRooted : Gets a value indicating whether the specified path string contains absolute or relative path information.
More information here:
http://msdn.microsoft.com/library/en-us/cpref/html/frlrfSystemIOPathClassTopic.asp