lucy24 - 8:44 am on Aug 14, 2011 (gmt 0)
On my own pages I tend to use two different forms of link highlighting: one for links that lead elsewhere on the site or even on the same page, another for external links. By now, all browsers make it easy to open links in a new window or tab if you prefer. So you don't have to force a choice on the user. Can't anyway, because even if you specify "_blank" they can change it in their prefs. At least to "new tab" instead of "new window".
Some sites do warn you when you click on an off-site link. "Are you sure you want to do this?" But all the examples I can think of are government sites where they can say with a straight face that the place you're going to may not be as reliable as the site you're currently on ;)