There are two main reasons people take on home improvement projects: for their own pleasure and in hopes of increasing the resale value of their homes. As long as you spend time and money for the first reason, you'll be okay. It's when you start thinking more about the second reason that you may be in for a disappointment. Even if improvements add value to your home, few recoup the money they cost. For example, a swimming pool, which costs tens of thousands of dollars to install, adds little to no resale value to a home. People are turned off by the maintenance aspect, and parents with small children will worry about safety issues.
So, what improvements do add enough value that you'll come close to making back what you spend? It's the highly visible improvements that will help most. Unfortunately, the less visible ones don't impress. Replacing the roof or furnace, while they may need doing, won't convince a home buyer to pay more. Likewise, new energy-efficient doors and windows are not likely to recoup the cost of installation (However, if you are going to continue living in your home for the next few years, $1,000 spent on insulation and caulking existing windows and doors can help you save on your energy bills). The biggest home improvement you can do to impress homebuyers (and make them want to pay more) is one of the cheapest.
What are you looking for?