Some wikipedia analysis on each of the 20 managers. Note club apps/goals are league fixtures only.
Alex Ferguson (Forward): 0 caps for Scotland. Dunfermline 89 apps (66 goals), Rangers 41 apps (25 goals), Falkirk 95 apps (36 goals)
Roberto Mancini (Attacking Midfielder): 36 caps for Italy (4 goals). Sampdoria 424 apps (132 goals), Lazio 87 apps (15 goals)
Andre Villas-Boas (Position unknown): 0 caps for Portugal, no professional clubs.
Rafa Benitez (Sweeper): 0 caps for Spain. Real Madrid Castilla (Real Madrid's reserve side) 247 apps (7 goals)
David Moyes (Centre Back): No caps for Scotland. Celtic 24 apps (0 goals), Dunfermline 105 apps (13 goals), Preston North End 143 apps (15 goals)
Arsene Wenger (Defender): No caps for France. Strasbourg 11 apps (0 goals).
Steve Clarke (Defender): 6 caps for Scotland. St Mirren 200 apps (7 goals), Chelsea 330 apps (7 goals)
Brendan Rodgers (Defender): 0 caps for Northern Ireland. No club stints of note.
Michael Laudrup (Attacking Midfielder): 104 caps for Denmark (37 goals). Juventus 102 apps (16 goals), Lazio 60 apps (9 goals), Barcelona 167 apps (49 goals), Real Madrid 62 apps (12 goals)
Tony Pulis (Defender): No caps for Wales. Bristol Rovers 130 apps (5 goals) - over two stints.
Sam Allardyce (Defender): No caps for England. Bolton 198 apps (21 goals) - over 2 stints, Preston North End 93 apps (2 goals) - over 2 stints, Millwall 63 apps (2 goals)
Chris Hughton (Fullback): 53 caps for Republic of Ireland (1 goal). Tottenham 297 apps (12 goals), Westham 32 apps (0 goals)
Martin Jol (Midfielder): 3 caps for Netherlands. ADO Den Haag 267 apps (15 goals) - over 2 stints, Twente 71 apps (9 goals), West Bromwich Albion 63 apps (4 goals)
Martin O.Neill (Midfielder): 64 caps for Northern Ireland (8 goals). Notts Forest 285 apps (48 goals), Fulham 94 apps (27 goals), Norwich City 66 apps (12 goals) - over 2 stints
Alan Pardew (Midfielder): No caps for England. Crystal Palace 128 apps (8 goals), Charlton 104 apps (24 goals)
Paul Lambert (Midfielder): 40 caps for Scotland (1 goal). St Mirren 227 apps (14 goals), Motherwell 103 apps (6 goals), Borussia Dortmund 44 apps (1 goal), Celtic 193 apps (14 goals)
Nigel Adkins (Goalkeeper): No caps for England. Tranmere Rovers 86 apps (0 goals), Wigan Athletic 155 apps (0 goals)
Roberto Martinez (Defensive Midfielder): No caps for Spain. Wigan Athletic 187 apps (17 goals), Swansea City 122 apps (4 goals)
Brian McDermott (Midfielder): No caps for England. Arsenal 61 apps (12 goals), Exeter City 68 apps (4 goals), Yeovil Town 62 apps (12 goals)
Harry Redknapp (Midfielder): No caps for England. Westham 149 apps (7 goals), Bournemouth 101 apps (5 goals)
And also the managers already sacked this season:
Roberto Di Matteo (Midfielder): 34 caps for Italy (2 goals). Lazio 87 apps (7 goals), Chelsea 119 apps (26 goals)
Mark Hughes (Forward): 72 caps for Wales (16 goals). Manchester United 345 apps (120 goals) - over 2 stints, Barcelona 28 apps (4 goals), Chelsea 95 apps (25 goals), Southampton 52 apps (2 goals), Blackburn 50 apps (6 goals).