The Länder-Tickets allow you unlimited travel with almost all regional trains within a specified area for a whole day. Some allow to use local transport in a few select regions.
The tickets are (with very few exceptions) not valid in inter-city services (train numbers starting with ICE, IC, EC, TGV, THA, RJ, EN, CNL, HBX, X). DB regional trains generally accept the tickets. Also the tickets are valid for most but not all private operators in the area. Where not specifically noted the tickets are not valid for local transport (e.g. busses, trams, U-Bahn), only trains (including S-Bahn).
The tickets are valid from 9am to 3am the next day (Mo-Fr). On weekends and public holidays they are valid from midnight to 3am the next day.
The details depend on the ticket you choose. The prices reflect the time of writing and are given as 1/2/3/4/5 persons. Most tickets have a surcharge if bought at a counter.
Also included are similar, Germany-wide tickets but not all special tickets (night tickets, first-class tickets, etc.).
Note for mobile users: Many of the links go to huge PDF files.
Schleswig-Holstein-Ticket
28/31/34/37/40€, covered routes
The ticket is valid in the states of Schleswig-Holstein, Mecklenburg-Vorpommern, and Hamburg. Additionally on a few select routes in Lower Saxony, Denmark, and Poland. Also valid on U-Bahn, ferries, and busses (not Schnellbus) in Hamburg (rings A and B).
Mecklenburg-Vorpommern-Ticket
23/27/31/35/39€, covered routes
The ticket is valid in the states of Mecklenburg-Vorpommern and Hamburg. Additionally on a few select routes in Schleswig-Holstein, Brandenburg, and Poland. Also valid on U-Bahn, ferries, and busses (not Schnellbus) in Hamburg (rings A and B).
In the following trains between Szczecin Glowny and Pasewalk the ticket is valid even before 9am: RE 5350, RE 5351, RE 5352, RE 5353, RE 5354
Niedersachsen-Ticket
23/27/31/35/39€, covered routes, map
The ticket is valid in the states of Lower Saxony, Bremen, and Hamburg. Additionally on a few select routes in Nordrhein-Westfalen and Hesse. Also valid on U-Bahn, ferries, and busses (not Schnellbus) in Hamburg (rings A and B). Additionally valid for all local transport in the GVH region (main city: Hannover), VRB region (main city: Braunschweig), VBN region (main cities: Bremen, Oldenburg), and VSN region (main city: Göttingen). In Osnabrück valid on busses (VOS zone 100).
The ticket is also valid on all IC trains on the route between Bremen Hbf and Augustfehn. From December 24 to December 31 valid from midnight until 3am next day.
Brandenburg-Berlin-Ticket
29/29/29/29/29€, covered routes, map
The ticket is valid in the states of Brandenburg and Berlin, including all local transport (except the SRS tram in Rüdersdorf/Schöneich). Additionally on a few select routes in Mecklenburg-Vorpommern, Sachsen-Anhalt, Saxony, and Poland.
Also valid on a few IC and EC trains.
If traveling alone a VBB Gesamtnetz ticket for 21€ is cheaper, but it has different conditions.
Schöner-Tag-Ticket NRW
29/42/42/42/42€, covered routes, map
The ticket is valid in the state of Nordrhein-Westfalen, including all local transport. Additionally on a few select routes in Lower Saxony, Hessia, Rhineland Palatine, and the Netherlands.
Hessenticket
33/33/33/33/33€, covered routes, map
The ticket is valid in the state of Hessia, including all local transport. Additionally on a few select routes in Nordrhein-Westfalen, Lower Saxony, Thuringia, Rhineland Palatine, and Baden-Württemberg.
Sachsen-Anhalt-Ticket, Thüringen-Ticket, Sachsen-Ticket
23/27/31/35/39€, covered routes, map
Those tickets are basically the same.
The ticket is valid in the states of Sachsen-Anhalt, Thuringia, and Saxony. Additionally on a few select routes in Brandeburg, Hessia, and the Czech Republic.
The ticket is also valid for local transport in the following areas: marego (main city: Magdeburg), MDV (main cities: Leipzig, Halle), VMS (main city: Chemnitz), VMT (main cities: Erfurt, Weimar, Jena), VVO (main city: Dresden), VVV (main city: Plauen), ZVON (main cities: Görlitz, Bautzen, Zittau). Also valid in Sachsen-Anhalt on <O> busses.
Rheinland-Pfalz-Ticket, Saarland-Ticket
24/28/32/36/40€, covered routes
Those tickets are basically the same.
The ticket is valid in the states of Rhineland-Palatine and Saarland, including all local transport. Additionally on a few select routes in Baden-Württemberg, Nordrhein-Westfalen, and France.
Baden-Württemberg-Ticket
23/28/33/38/43€, covered routes, map
The ticket is valid in the state of Baden-Württemberg. Additionally on a few select routes in Bavaria, Hessia, Rhineland Palatine, and Switzerland.
The ticket is also valid on almost all local transport, except busses between Ulm and Neu-Ulm and ferries on Lake Constance.
Bayern-Ticket
23/28/33/38/43€, covered routes, map
The ticket is valid in the state of Bavaria. Additionally on a few select routes in Baden-Württemberg, Thuringia, and Austria.
The ticket is also valid on almost all local transport, except busses on this list.
Quer-durchs-Land-Ticket
44/52/60/69/76€, covered routes
The ticket is valid in all of Germany. Additionally on a few select routes in Austria, Switzerland, and Czech Republic.
Schönes-Wochend-Ticket
40/44/48/52/56€, covered routes, map
Only available for Saturday and Sunday.
The ticket is valid in all of Germany. Additionally on a few select routes in Denmark, the Netherlands, Austria, Poland, Switzerland, and Czech Republic.
In many areas the ticket is also valid for local transport, see the covered routes link.