The first thing I discovered was the new Marketplace client that brings an 'App Store' like experience to Eclipse. Finding and installing components has always been a challenge, but with the Helios release this will all change.
The Marketplace Client makes it easy to browse and install 3rd party components. Available under Eclipse -> Help, this new feature should make it much easier to find the tools you need
I haven't got time to test the lot of new features shipped in Helios, but here are some of my favorite features:
The Open Implementation command is available from the Navigate menu. A key binding can be assigned on the General > Keys preference page.
I use CTRL + click
Another feature I liked is that javadoc hovers now render {@value} inlined
You can find this 2 features among many here:
http://download.eclipse.org/eclipse/downloads/drops/R-3.6-201006080911/eclipse-news-part2.html
and here:
http://download.eclipse.org/eclipse/downloads/drops/R-3.6-201006080911/eclipse-news.html
