In my opinion, Richfaces works best with Seam as it is tested very well, we have built a huge application based on Richfaces and it works perfectly,
I think the integration between RF and Ajax4Jsf is best and you can find beneficial from both world together and combine nice stuff with RF/a4j, more than that, it's all under the same house which is important if you plan to purchase support some when,
Regarding your question, I also tested Myfaces / Icefaces with Seam and it worked very nice as Seam is not binded in any way to RF or any other specific JSF components library, in a matter of fact, I sometimes I use Seam without any relationship to the JSF world :-)
Well, check the examples, Icefaces works and it's active, same goes for Trinindad,Myfaces (I tested it very long time ago but it might still work),
There are very very nice components library named 'Woodstock', but I have encountered many problems while trying to use them with Seam,
I think Gavin somewhere before a year replied me that they are working on it together to make Woodstock work with Seam but I didn't see anything new about it(but I might be wrong),
Well, at the end, after all the nice specs and standards, Seam works best under Jboss, RF works best with Seam/Jboss, Woodstock works best with Glassfish, Oracle goes with Trinidad and thats the way it works,
(I'm not saying they cannot be combined, I just say it's harder)
Well, at least that is from my own experience :-)
I began to use the ICEfaces with Seam when ICEfaces just became open source and Gavin announced to support ICEfaces with Seam. I found that Seam works very well with ICEfaces. I never tried the Richfaces, but I know that Richfaces should work more well with Seam, since JBoss own the Richfaces. A little annoying thing when using ICEfaces is that some components of Seam, e.g. s:fileUpload, seam email, still don't work with ICEfaces. Maybe, it can be solved in the near future.
Personally, I hope that Seam can fully support some MAIN jsf frameworks, since Seam seems to be the dominate Java EE framework in the future (my own opinion).
so, did any of you try Seam/Richfaces tree with interactive features (click on expanded node)?
I see the Seam-built new SeamFramework.org without any tree structure. Guess people already know something about it.
How about GWT? some brave souls has attempted, but the conversion is not propagated there yet.