What programming interest specifically do you have? Device drivers? Kernel/service modules? Single/Multi-threaded? Firmware? GUI? Gaming? Demo/Multimedia? Audio? Video? Software plugins?
How about project size? Project role? Project difficulty? Project depth and dimentions? How long do you want to spend on it? A role involving applying updates? Debuging? Testing?
Do you want money for it? Perhaps want to just practice your skills? You can jump into many open source C projects to add features or fix existing bugs.
Your question attracted my attention because, as Narue alluded to, its so tremendously unspecific that google would be your best starting point. Once you know what you think you want to do, type in a few keywords in google and you might find what you are looking for. Many current projects are still being made in C, but its usually found in low to medium level projects.
Personally, I use C mixed with a few high level languages in my projects. For instance, my designs are in XML and my database work is in SQL.