Free at last, free at last! JRockit is no longer tied to Oracle products: you can download it for what look like the same terms as the old Sun JDK. JRockit is way faster then HotSpot after a suitable warmup period.
That entry says it's the same terms as the Oracle JDK that used to be the Sun JDK.
In my experience, like the summary says, JRockit is superfast after a while - generally when about an hour passes, it JITs stuff really well. That means for short term apps, you might want to use the Sun JVM, and for server apps, JRockit is the way to go.
JRockit's GC is really nice, too; it can be made predictable, which is something that's bugged the Sun JVM users for years. Look at BigMemory, which was created as a response to the Sun JVM's lame GC process and how hard it is to tune the GC.
Mission Control and Realtime still are commercial offerings. Well worth it, though, and I'm really happy to see JRockit free. Looks like you need an Oracle Network login to get it, still, though.