Updated @gruber's regex with a modified version that looks for 2-13 letters rather than trying to look for specific TLDs. Given the recent addition of ~1400 gTLDs, it may be time to give up on that front. (UPDATE 2018-05-15: Naked URLs without protocol prefix now capable of matching more advanced URLs. Also escaped / and " so it's easier to copy…

Liberal Regex Pattern for URLs

# Single-line version:
(?i)\b((?:https?:(?:\/{1,3}|[a-z0-9%])|[a-z0-9.\-]+\.(?:[a-z0-9]{2,13})\/)(?:[^\s()<>{}\[\]]+|\([^\s()]*?\([^\s()]+\)[^\s()]*?\)|\([^\s]+?\))+(?:\([^\s()]*?\([^\s()]+\)[^\s()]*?\)|\([^\s]+?\)|[^\s`!()\[\]{};:'\".,<>?«»“”‘’])|(?:(?<!@)[a-z0-9]+(?:[.\-][a-z0-9]+)*[.](?:[a-z0-9]{2,13})\b\/?(?!@)(?:[^\s()<>{}\[\]]+|\([^\s()]*?\([^\s()]+\)[^\s()]*?\)|\([^\s]+?\))+(?:\([^\s()]*?\([^\s()]+\)[^\s()]*?\)|\([^\s]+?\)|[^\s`!()\[\]{};:'\".,<>?«»“”‘’])))

# Commented multi-line version:

(?xi)
\b
(                                         # Capture 1: entire matched URL
  (?:
    https?:                               # URL protocol and colon
    (?:
      \/{1,3}                             # 1-3 slashes
      |                                   #   or
      [a-z0-9%]                           # Single letter or digit or '%'
                                          # (Trying not to match e.g. "URI::Escape")
    )
    |                                     #   or
    [a-z0-9.\-]+\.                        # looks like domain name
    (?:[a-z0-9]{2,13})                    # ending in common popular gTLDs (or final octet of IPv4 IP)
   \/                                     # followed by a slash
  )
  (?:                                     # One or more:
    [^\s()<>{}\[\]]+                      # Run of non-space, non-()<>{}[]
    |                                     #   or
    \([^\s()]*?\([^\s()]+\)[^\s()]*?\)    # balanced parens, one level deep: (…(…)…)
    |
    \([^\s]+?\)                           # balanced parens, non-recursive: (…)
  )+
  (?:                                     # End with:
    \([^\s()]*?\([^\s()]+\)[^\s()]*?\)    # balanced parens, one level deep: (…(…)…)
    |
    \([^\s]+?\)                           # balanced parens, non-recursive: (…)
    |                                     #   or
    [^\s`!()\[\]{};:'\".,<>?«»“”‘’]       # not a space or one of these punct chars
  )
  |                                       # OR, the following to match naked domains:
  (?:
    (?<!@)                                # not preceded by a @, avoid matching foo@_gmail.com_(?<![@.])
    [a-z0-9]+
    (?:[.\-][a-z0-9]+)*               
    \.                                    # avoid matching the last two parts of an email domain
                                          # like co.uk in person@amazon.co.uk
    (?:[a-z0-9]{2,13})                    # ending in common popular gTLDs (or final octet of IPv4 IP)
    \b
    \/?
    (?!@)                                 # not succeeded by a @, avoid matching "foo.na" in "foo.na@example.com"
    (?:                                   # One or more:
      [^\s()<>{}\[\]]+                    # Run of non-space, non-()<>{}[]
      |                                   #   or
      \([^\s()]*?\([^\s()]+\)[^\s()]*?\)  # balanced parens, one level deep: (…(…)…)
      |
      \([^\s]+?\)                         # balanced parens, non-recursive: (…)
    )+
    (?:                                   # End with:
      \([^\s()]*?\([^\s()]+\)[^\s()]*?\)  # balanced parens, one level deep: (…(…)…)
      |
      \([^\s]+?\)                         # balanced parens, non-recursive: (…)
      |                                   #   or
      [^\s`!()\[\]{};:'\".,<>?«»“”‘’]     # not a space or one of these punct chars
    )
  )
)