Spain:
While Spain is dominant in club football, leading the coefficient table by a mile, the national team hasn't been that successful since winning the 2012 edition of this tournament. Xavi retired after the disastrous World Cup which saw Spain go out in the group stage as defending champion. The same fate seems less likely for 2016 though, given the pretty fair group they got. The players are almost exclusively part of top clubs in Spain and England, with Thiago, Casillas and Morata being notable exceptions. They also won their qualifying group pretty convinicingly, with 9 wins and a single loss to Slovakia, hoping to use this momentum™ to recreate their 2012 performance instead of going out early like in Brazil.
Czech Republic:
The Czechs have a relatively old squad, which consists of many domestic league players (mostly from Plzen and Sparta Prague) but also featuring Rosicky (if he's not injured) and Petr Cech, who's one game away from being the sole most-capped player for his country, overtaking Karel Poborsky (both currently have 118 caps each). I also learned that Bremen's Gebre Selassie is apparently Czech. The team qualified for France by winning Group A ahead of Iceland. They will probably fight for second place in the open group.
Turkey:
Another qualifier from Group A - Turkey finished third, and qualified directly for being the best third placed-team. Their current squad appears to be Domestic league player + Arda Turan + Nuri Sahin. Most of the players obviously play for the Istanbul clubs Galatasaray, Besiktas and Fenerbahce. The bookies seem to rate them on par with the Czechs, which could lead to interesting scenarios on the last matchday.
For Turkey, it will be the first international tournament after the 2008 Euro, in which they finished third after getting knocked out in a dramatic semifinal against Germany. It seems unlikely that they will repeat this performance in France.
Croatia
Croatia are regular guests at the european championships, missing the tournament just once since splitting from Yugoslavia in the mid-90s. This tyme they qualified by finishing second to Italy in their qualifying group, overtaking Norway on the last matchday. Most of their squad play outside of Croatia, with Modric and Rakitic being Clasico rivals and Mandzukic playing for Juventus. Former Bayern player Daniel Pranjic also still seems to be playing at age 34. They can be considered second favourites in Group D.
DER MARKT:
To win the group: Spain 1.73, Croatia 4.5, Czech Republic 10, Turkey 12
To qualify: Spain 1.15, Croatia 1.44, Turkey 1.91, Czech Republic 2.25
To win the tournament: Spain 7, Croatia 34, Turkey 91, Czech Republic 126
Schedule:
June 12, 15:00 CEST: Turkey v Croatia
June 13, 15:00 CEST: Spain v Czech Republic
June 17, 18:00 CEST: Czech Republic v Croatia
June 17, 21:00 CEST: Spain v Turkey
June 21, 21:00 CEST: Croatia v Spain, Czech Republic v Turkey