Rayner made his Sussex debut in 2006 after working his way through the ranks at the county.
He is a tall offspinner, standing at 6ft 5in, and a useful batsman - scoring a century on debut against the visiting Sri Lanka side.
He played one championship match in 2007 as Sussex clinched the title for the second successive year.
He was more used in one-day cricket, playing six Friends Provident Trophy games and five Twenty20 Cup matches.
With first-choice spinner Mushtaq Ahmed injured for much of 2008, Rayner played a much more prominent role for Sussex.
He took 31 wickets in Division One of the LV County Championship and was rewarded with a new two-year contract.