In short, these are the basic powers and checks for each branch of the government:

Executive Powers (Presidential)

Approves or vetoes federal bills
Carries out federal laws
Appoints judges and other high ranking officials
Makes foreign treaties
Can grant pardons and reprieves to federal offenders
Acts as commander in chief of the armed forces

Checks on Executive Powers

Congress can override vetoes by a two-thirds vote
The Senate can refuse to confirm appointments or ratify treaties
Congress can impeach and remove the president
Congress can declare war
The Supreme Court can declare executive acts unconstitutional

Legislative Powers (Congressional)

Passes federal laws
Establishes lower federal courts and the number of federal judges
Can override the presidents veto by a two-thirds vote

Checks on Legislative Powers

Presidential veto of federal bills
Supreme Court can rule laws unconstitutional
Both houses of Congress must vote to pass laws, checking power within the legislature

Judicial Powers

Interprets and applies the law by trying federal cases
Can declare laws passed by Congress and executive acts unconstitutional

Checks on Judicial Powers

Congress can propose constitutional amendments to over-turn judicial decisions. These require a two thirds majority in both houses, and ratification by three-quarters of states.
Congess can impeach and remove federal judges
The president appoints judges, who in turn must be confirmed by the senate