This tool has been around for quite some time, but it often surprises me how few people (also ‘professional’ ones) seem to have heard about it. Since it’s the only FREE live CSS IE editing tool I know, and since (added bonus!) it actually offers split-view Firefox/Internet Explorer editing, there’s no harm in spreading the word a bit.
Get it at: http://litmusapp.com/labs. DL link is sent to email address provided. However, I’m pretty sure they honour their no-spam policy.
Oh yes… it only runs on windows. But since there’s no escape having to consider IE users browsing your site, it’s almost worth keeping a windows installation for (that, and homebanking).
Tip: If your site requires a login and you have problems logging in using CSSVista: save the page you want to edit using Firefox and open it in CSSVista for editing.
And just in case you’ve been hiding under a rock, for day-to-day live CSS editing use (running fine under Linux!) there’s the webdev swiss army knife: Chris Pederick Web Developer Extension.