If anyone is looking for an easy to use and customizable sound effects player, check out the RaceFX Sound Effects Player software at http://grandprix-software-central.com/rcfx/
+ Play any WAV, MID, MP3, AIF, AIFF, AU, or WMA sound files
+ Play sounds with the click of a button or press of a keyboard shortcut
+ Loop sounds
+ Overlap sounds
+ Create a play list of sounds to play sequentially
+ Organize sounds into different categories
+ Customize any of the sound button images with BMP, GIF, ICO, JPG, PNG or WMF images of your own
+ and more...
You should also try SoundBites v2.2, it does all that RaceFX does and lots more. There is an integrated CD ripper, sound effect recorder, an editor to enable you to play sections of tracks and loads more.
Download a free 30 day trial from www.minstrelmediasoftware.co.uk
Both of these are PC only, I assume?
If you-re after a Mac solution try Qlab. Free and flexible. And verz reliable.
Not as a performance software but more of a preview software, especially for loops, I used to use the open source player Aqualung on Linux (Win/OSX supported as well) because it features gapless playback and is rather minimalistic.
I haven't figured out enough of its shortcuts though and mostly play sounds in the command line using mplayer if I'm not sure what they are and then just load them into audacity.
Aqualung is a very sleek player, but it also has some power under the hood; a feature probably not very useful when Aqualung is used as a music player, but that can speed up sound processing along with Audacity, is the FX section.
You can load multiple Linux native plugins and even Windows VSTs and twiddle their parameters in real time while the sound plays, and that helps experimenting more quickly than Audacity's short preview window before applying a single effect.
Sort of what you'd do on an audio track channel of a full fledged DAW, but with the speed and lightweight of a sound player.