If you’re only resizing images about 200% or so, Adobe Photoshop’s own algorithms work just fine. Simply choose Image > Image Size and enter your new dimensions. Bicubic is a good overall choice, while Bicubic Smoother is good for enlarging and Bicubic Sharper for reducing image size. If you’re going larger, it’s time to consider a plug-in, and you have a wealth of choices available to you. To be honest, they all do a good job, but when it comes to our images, good is seldom good enough – we want the best and nothing less.
Over the years, I’ve used Fred Miranda’s Resize actions, Photozoom Pro, Blow-up, and Genuine Fractals. I always shied away from the early versions of Genuine Fractals though because I didn’t want to deal with a proprietary file format and the hassles that involved. Newer versions though have eliminated the need to save as a .STN file. Sure, it greatly reduces the size of the scaled image, but it’s one more step in my workflow, and I have enough of those.
