Official site for Mandelbulb3D:

Download site for Mandelbulber, a 3D open source fractal program. Works on Windows, Mac and Linux:

Fragmentarium 2.5 is a 3D fractal program derived from the original Fragmentarium project: Fragmentarium

JWildfire is a popular fractal-flame based program done in Java. His author also keeps MB3D alive: Jwildfire

Fractal Forums

Incendia Next. An awesome 3D fractal app. Incendia Next.