I’ve become a big fan of Leaflet for putting maps on the web. It gives me most of what I need without much of what I don’t and is fairly easily extended, as shown by the impressive work of Jason Sanford.
A while back, Dave Bouwman blogged about work he and the team at DTS Agile had done extending Leaflet to support ArcGIS Server layers. Given that there are a lot of ArcGIS Servers out there, this is a good thing to have. Thanks to section 4(f) of the Esri Web Services Terms of Use, it’s less useful for use with ArcGIS Online, but that’s probably the topic of another post.