I've had success in the past closing gaps on laminate flooring using a bulldog type tool, that grips onto the board and allows you to move the piece of flooring by tapping the tool with a mallet. It's a bit risky, as there is potential to break the edges of the boards, so I'd only recommend it if:
1) You really know what you're doing
OR
2) You're planning to replace the floor if you can't fix it to your satisfaction.
This isn't quite the one I've used, but similar.
http://www.torlys.com/installation/bulldog
(I should mention #2 applied to me, not #1...)