What British Document provided an important model for the Americans?

Answer 1

No,not Magna Carta. Rather, the English Bill of Rights, 1689.

This document and the Declaration of Independence fulfilled a similar function, and that the Declaration, as well as several other colonial documents, drew on the model of the Bill of Rights.

In particular the Bill of Rights was written by Parliament at the time of the Glorious Revolution to justify its action of REJECTING the rule of James II and installing William and Mary in his place. A major section of the document is a list of alleged abuses of the king, violations of British (esp Parliamentary) rights. In the same way, the heart of the Declaration (and other colonial documents) is a list of British ABUSES, esp. those of King George, that are offered as justification for rejecting HIS rule and declaring independence.

In fact, you can compare a number of specific points of language in the two, esp in the lists of particular charges/justifications against the kings.

Here are perhaps the closest parallels (in each case, the first is from the Bill of Rights, the rest from the Declaration of Independence)

By raising and keeping a standing army within this kingdom in time of peace without consent of Parliament, and quartering soldiers contrary to law
* He has kept among us, in times of peace, Standing Armies without the Consent of our legislatures.

By assuming and exercising a power of dispensing with and suspending of laws and the execution of laws without consent of Parliament;
* He has dissolved Representative Houses repeatedly, for opposing with manly firmness his invasions on the rights of the people.
* For suspending our own Legislatures, and declaring themselves invested with power to legislate for us in all cases whatsoever

By violating the freedom of election of members to serve in Parliament;
* He has refused for a long time, after such dissolutions, to cause others to be elected, whereby the Legislative Powers, incapable of Annihilation, have returned to the People at large for their exercise;

By levying money for and to the use of the Crown by pretence of prerogative for other time and in other manner than the same was granted by Parliament;
* For imposing Taxes on us without our Consent:

By prosecutions in the Court of King's Bench for matters and causes cognizable only in Parliament, and by divers other arbitrary and illegal courses;
* For depriving us in many cases, of the benefit of Trial by Jury:
* For transporting us beyond Seas to be tried for pretended offences


See the English Bill of Rights -
http://www.yale.edu/lawweb/avalon/england.htm

Declaration of Independence ("indictment" section):
http://en.wikipedia.org/wiki/United_States_Declaration_of_Independence#Indictment

See also:
http://en.wikipedia.org/wiki/Bill_of_Rights_1689

As for other (earlier) colonial documents that echo the English Bill of Rights, check the various STATE constitutions and declarations of independence, such as the first constitution of the state of Virginia (the 'grievance' section and thereafter drafted by Jefferson, the earlier parts by George Mason):
http://www.teachingamericanhistory.org/library/index.asp?document=105

Also the"Declarations and Resolves" of the FIRST Continental Congress in October 1774 --
http://www.yale.edu/lawweb/avalon/resolves.htm

Answer 2

Magna Carta.