Khan Academy offers video tutorials and guided exercises for many types of word problems appropriate to students in grades 3-12.  The problems involve skills in basic number operations, fractions, ratios, age, multi-step, averages, rational numbers, coordinate planes, absolute value, money and decimals. If you get stuck while working a guided exercise word problem, you can request a hint.  Up to 3 are available for each problem, as well as videos of similar problems.

If you register for free, you can see what skills you’ve mastered and keep track of what problem-solving skills come next.

From site:

From 1999-2002, Making Mathematics matched students and teachers in grades seven through twelve with professional mathematicians who mentored their work on open-ended mathematics research projects. Although our project has ended, we encourage you to look through our mathematics projects, teacher handbook, and mentor handbook [PDF] for information on pursuing mathematics research projects with middle- and high school students.

There are 12 complex problems. They deal with number theory, algebra, calculus, geometry, patterns and reasoning. Each problem has warm-up problems and hints to help with the solution. There are also extension problems related to the original problem. So that actual number of problems available is much more than 12.

Math Playground has word problems for students in grades 2-8. The problems for grades 2-5 are incorporated in games. To help teach solving skills, there are video explanations and interactive thinking blocks, virtual manipulatives to help kids visualize the equations.

KidZone has word problems by grade level, grades 1-5, and theme. The themes include the seasons and holidays. Each time you select a problem a new problem is generated using the same scenario with different numbers. This gives kids added practice at reading the verbal clues.

Practical Uses of Math and Science, PUMAS, is a collection of 90 examples showing how math and science topics taught in grades 9-12 can be used in interesting settings, including every day life. These examples are written primarily by scientists, engineers, and other content experts having practical experience with the material. NASA’s goal is to capture for high school students how what they learn in math and science is used by working scientists.