I think that Visual Studio\'s biggest let down is the Javascript editor. I have been told to use Aptana as an editor for my javascript files, but I would prefer to stick with v
VS is a pretty good IDE (especially when coupled with Resharper) but not so hot with Javascript. The debugger is good and there's the JSLint plugin but other than that I'm not sure. Aptana (based on Eclipse) is an excellent javascript IDE but it doesn't like it much when the javascript is embedded in aspx files (unless they updated the support recently). So far I'm not sure there's an ideal .net platform IDE for both client and server side stuff just yet.
Update: Resharper 6 added pretty good JavaScript support - so now I'd recommend that combination if you're doing a lot of debugging across client and server at the same time. If you're focussing on pure client code then I find WebStorm to be an excellent JavaScript/HTML IDE - even better than Aptana.