Cliff Click has a terrific post on Java-vs-native-code performance . Recommended. Cliff is the Chief JVM Architect at Azul Systems, was the lead designer behind Hotspot's server JIT compiler, and is an all-around smart guy. His main drawback is that he (apparently) gets dragged into flamewars on YouTube's comment section.
Jeremy Manson's blog, which goes into great detail either about concurrency in Java, or anything else that the author happens to feel is interesting or relevant to the target audience.