Jens Lehmann
Arsene Wenger signed this charismatic goalkeeper from the German club Schalke 04 in the summer of 2003 as a replacement for David Seaman and Lehmann was the custodian for the English club when they achieved their unbeaten season in EPL 2003-2004.
He played till 2008 for the English club, putting together an EPL career consisting of one League Title and one FA Cup triumph. Jens Lehmann bid adieu to the club in 2008 when he signed an one year contract with VfB Stuttgart. But this was not the end as the German goalkeeper resigned with Arsenal in 2011 after insistence from Arsene Wenger, who faced a major crisis due to injuries of the existing squad goalkeepers.
Though he managed only one start in this stint, the Jens Lehmann transfer was a huge boost to the team morale.
Thus, it can safely be said that players coming back for a second spell in Arsenal is quite common under the Wenger reign and it is left to be seen how much difference the re-signing of Mathieu Flamini makes to the future of the Gunners.
P.S. Arsenal legend John Lukic joined the Gunners for the second time two months before the appointment of Arsene Wenger in 1996. The legendary goalkeeper played 223 matches between 1983 and 1990 for the London club during his first stint.