MacOSaiX is an application designed to generate mosaics quickly and effortlessly. It does that within a user-friendly interface with multiple customization settings to choose from, support for multiple image sources and what's more, this is completely free to use.
The utility requires you to input an image; a picture with less details will need less tiles than a larger, high quality one. Based on that, start adding pictures from the Image Sources panel. This is where MacOSaiX really shines as it supports queries to multiple online image websites: Google Image Search, Delicious Library, flickr, Glyphs, iTunes. Select the shape of the tiles (rectangular, hexagonal, puzzle pieces), specify the size and image usage.
Individual tiles may be selected from the output mosaic and replaced with other images.
MacOSaiX allows users to save their work as projects which may be loaded at a later time.
Program preferences deal with the amount of images that will be stored on the user's computer after retrieving via the flickr and Google Image Search services.
MacOSaiX is flexible, quite intuitive to use and effective; in addition to that, it's free of charge.