- Infragistics (http://www.infragistics.com/)
- Telerik (http://www.telerik.com/)
- ComponentArt (http://www.componentart.com/)
- Framework is not sufficiently exhaustive to cover 99% of the requirements;
- Vendor has not been around for a sufficiently long time;
- Updates are not sufficiently frequent to follow the pace of new developments like Ajax;
- Developer license is not royalty-free and/or price is unaffordable;
On the mid-term, ComponentArt may have taken a competitive edge by rewriting its components on top of the Microsoft Ajax framework (code-named Atlas).
On the long-term, it is difficult to predict the impact of WPF on web interfaces. On one hand, there is a need for richer interfaces that are easier to develop and Microsoft is committed to deliver the technology (WPF/E) and tools to achieve just that. On the other hand, WPF is really nothing more than Flash the Microsoft way, and very few web sites are developed with Flash yet although the Flash plug-in is available on 90% of internet PCs.
I have personally used Sheridan and now Infragistics controls for years, so I stick with them but if I had to make a new choice now, I would definitely opt for the rewritten ComponentArt controls.