I deleted most of my PMI and SamleTekk libraries; just not detailed enough (except for SampleTekk's marimba and renaissance recorders, and PMI's anvils and carillon, which fill some gaps not covered or not covered well by VSL).
For accordions, I highly recommend NUSofting Peti, which is based on FM technology. But you'll have to take some time with it, as it doesn't ship with any presets (at least on the Mac AU version). I made a few of my own for Italian Accordion, Indian Harmonium, etc.
Library-wise, Precisionsound has by far the most varied and detailed accordion samples these days. These have come around in just the last couple of years, so are not all that well-known yet. There is quite a variety of different sounds and styles. Their sale just ended, but they have sales frequently.
On the whole though, I am finding that the non-sample-based NUSofting Peti sits in the mix the best with Vienna Instruments winds, brass, strings, and percussion.