I often need to audition audio files or compare different sources. I used to have a generic session in my DAW for this, but that became unmanageable. There were simply too many sample-rates, formats, and variables to rely on a single generic file. Fortunately, I found a great application that offers high-quality playback and a lot more. JRiver Media Center is one of the most comprehensive audio/video players available. Originally Windows-only, a Mac OS version was released recently.
Media Center is a pro-level application disguised as an audiophile player. The reason I am enthusiastic about a program that plays audio (unlike iTunes or some free applications), is because Media Center retains your high-resolution format. In other words, it plays bit perfect. For example, you can use 16bit CDs, 24bit fixed or 32bit floating-point audio files, and various sample-rates (88.1 kHz, 176 kHz, etc.); plus it plays DSD through compatible DACs. There is no Windows WDM sample-rate conversion, no library import, and no system utility changing anything. The source code is 64bit floating point, and since we work with 24bit DAC units, Media Center has an additional 240 dB of precision workspace beyond the hardware's output. This leaves open the possibility of using digital volume, room correction, and other functions without clipping your converter. It supports all lossless formats of audio (FLAC, APE, ALAC, WM), as well as AIFF and WAV files (including tagging). Want to grab something from Bandcamp? No problem, just play it in its native format. For example, Toad the Wet Sprocket's album New Constellation in 24/96 FLAC on SoundCloud - I can play it right now, and no conversion required.
A big plus for me is native ASIO support, which is the driver of choice for professional Windows users. This allows JRiver Media Center to stream directly through my interface and into the mastering DAC of my choice. It can also play from RAM and help with speaker calibration for stereo or 5.1; and it even includes analysis tools such as spectrum and oscilloscope displays. When I was testing the Benchmark DAC2 HGC converter [Tape Op #97], I was able to play DSD files from Media Center straight to the Benchmark. While not all DACs support such acrobatics (only Mytek and Benchmark presently come to mind), this feature alleviates the need to buy a dedicated DSD player.
Since it is a "media" player, it includes many functions that may not apply to recording engineers: image galleries, video playback, network player, home theatre, etc. I consider those to be all bonuses. I really like that mix engineers can plug a USB drive into my computer and audition a 24bit, 96 kHz file without converting and importing it into a DAW session. Media Center also makes a great party shuffler that uses high-quality sources as opposed to lossy compressed files. I don't know how I got along without this on my PC. And now Mac users can get in on the fun. A free, 30-day demo is available for download.