I'm a big fan of CPU architectures. Here's a conversation between David Moon formerly of Symbolics Lisp Machines and Cliff Click Jr. of Azule Systems. They discuss details of both the Lisp Machine architecture and Azule's massively multi-core Java machine.
The claim (from both Symbolics and Azule) is that adding just a few instructions to an ordinary RISC instruction set can make GC much faster. With so much code being run in Java these days I wonder if we'll see similar types of instructions added to mainstream architectures.