Alviro Petersen will make Somerset his third county in as many seasons after signing a deal to play for them as their overseas player for the first part of the 2013 season.
Petersen will be available for Somerset until at least the start of the Friends Life t20 tournament, which is likely to be in mid-June.
Northamptonshire have appointed Stephen Peters and Alex Wakely as their captains for the 2013 season.
The duo will replace former South Africa all-rounder Andrew Hall, who was appointed in 2010 but has resigned in order to concentrate on his own game.
Lancashire have made Kabir Ali their first signing of the winter as they look to bolster a bowling attack that has already witnessed the departures of Naqaash Tahir, Gary Keedy, Sajid Mahmood and Ajmal Shahzad.
Rumours were doing the rounds as early as September about Surrey signing South African captain Graeme Smith and the club have now confirmed the left-hander as their new captain for the 2013 season as well as for the following two years.
It will be the 31 year-old's second spell in county cricket, after leading Somerset in 2005, a season in which they lifted the Twenty20 Cup for the first - and to date - only time.
The new structure is a result of the significant customer research that the ECB carried out at the end of last season, with the main changes being a switch back to 50-over cricket, the retention of the successful two-division 16-game County Championship formula with more consistent and Sunday start days, and the introduction of a season-long Twenty20 competition, played predominantly on Friday nights, rather that the current block format.
Surrey have further strengthened their spin bowling stocks by signing veteran Lancashire left-arm spinner Gary Keedy on a two-year contract. Plus news from Derbyshire, Nottinghamshire and Gloucestershire.
Nottinghamshire have strengthened their seam-bowling line-up following the close-season loss of Darren Pattinson by signing former Lancashire and Yorkshire all-rounder Ajmal Shahzad on a three-year contract. Plus news from Somerset, Leicestershire, Derbyshire and Sussex.