I realize that it's possible to integrate 3rd party controls; and it would be great if SF supported Infragistics Netadvantage the way it does DevExpress. Infragistics has the most consistent record of constant improvement (my opinion, but reflected in reviews also) among similar vendors.

Talk to them. We have tried to get their permission to create a wrapper and they have told us repeatedly that if we do it could get legal.  They say this is a violation of their licensing.  We do not want to distribute their DLLs, just create a wrapper for them like we did DevExpress.  We have tried to work with them over and over again, but they are very difficult. 

If they get bombarded enough by our users then possibly they may turn the corner and give us consent.  But until then there is nothing we can do. 

For whatever it is worth, we use the DevExpress controls for our medical system and they have been great!  Before we got into the whole "licensing" issue with Infragistics, we sat down corporately to evaluate all of the UI control options out there.  Infragistics had some good ideas in the their masking and they definitely have more in the charting area.  But as far as the grid and editors go, DevExpress won hands down.  And this is where a developer spends 90% of their time.  So we made the decision to go with DevExpress.  As for our charting needs, we have looked to Dundas.  Their charting controls are much more advanced than Infragistics or DevExpress.