Barker was voted the Cardiff City supporters' player of the season in 2004–05.
On 18 August 2006, Barker was signed on loan by Colchester United, until January 2007. This was later extended until the end of the season. Unfortunately, the move didn't become permanent at the end of his loan spell, but he is still regarded as a very popular and much respected player with the fans at Layer Road.
On the 9 August 2008, Barker signed an initial emergency loan deal for Plymouth Argyle, allowing him to make his Argyle debut later that day, with a starting place in the club's opening game of the 2008-09 season, against Wolverhampton Wanderers. Two days later, the signing was made permanent, with Barker signing a three-year contract, for an undisclosed fee.