Here are two of web-base color scheme/palette generators that I find I use whenever I need to come up with decent color scheme. You can really use them for either desktop or web apps when you need to find harmonious colors that go well together.
First is Color Scheme Designer. Super easy to use and has color simulation mode so you can see how your color scheme looks to people that are color blind.
Adobe kuler is another color scheme generator that is good if you are looking for pre-defined color schemes, there are ton of them there… You can create your own as well, but I think Color Scheme Designer is better fit for that task.