I compiled a list of some possible new context managers that could be added to the stdlib. Introducing a new feature should IMO also show usage of it in the distribution itself. That wasn't done with decorators (a decorators module is compiled at the moment, if I'm right), but with context managers, there's certainly room to add some. Of course, my list is excessive, it's only some ideas I got by flying over the stdlib docs.
* builtins: with open/file * sys: with sys.redirected_std[in|out|err] with sys.trace with sys.excepthook * warnings: with warnings.filter * pprint: with pprint.printer (used for print) * codecs: with codecs.open with codecs.EncodedFile * decimal: with decimal.Context * os: with os.current_directory with os.modified_env with os.umask/uid/gid etc. with os.popen with os.tmpfile * subprocess: with subprocess.Popen * mutex: with mutexobj * curses: with curses.wrapper * tempfile: with tempfile.[Named]TemporaryFile etc. * locale: with locale.differentlocale * logging: with logging.ignored with logging.Logger * signal: with signal.handler * socket: with socket.socket * threading: with threading.Lock with threading.Condition with threading.Event * mmap: with mmap.mmap * bz2/zipfile/tarfile: with ...open * dl: with dl.open * tty: with tty.raw with tty.cbreak * cgitb: with cgitb.enabled * urllib/urllib2: with urllib.urlopen etc. * httplib: with httplib.HTTPConnection * ftplib: with ftplib.FTP * poplib: with poplib.POP3 * imaplib: with imaplib.IMAP4 * nttplib: with nntplib.NNTP * smtplib: with smtplib.SMTP * telnetlib: with telnetlib.Telnet * xmlrpclib: with xmlrpclib.ServerProxy