Good audio reverb source?

Are you kidding? Reverb is the easiest thing in the world to do programatically:

for (int i = 0; i < input.Length; i++)
{
    output[i] += input[i];
    output[i + delay] += input[i] * decay; 
}

I write this kind of stuff full time now, so maybe it just seems easy. Do you mean you're looking for more general echo or spatial effects, that might include frequency-modulated delay lines and chorusing and so on?

How about this one? I know you said you didn't want freeverb, but this is episode 3 of freeverb, and to my eye it looks like it has been vastly improved.

_{(source: soundonsound.com)}

This version is a convolution reverb that supports impulse response. For those of you who don't know what that is, engineers take microphones into a space that they want to model (i.e. a performance hall) and fire a starter pistol, measuring the echoes produced. These echoes are then used to model the reverb. This process provides a very realistic reverb, that mirrors the characteristics of the performance hall.

http://freeverb3.sourceforge.net/