Syvecs is my prefered choice of ECU - very flexible with loads of great features. GTR / 350Z support will be out very soon. Its very popular on Subarus, Supras and TVRs. I've fitted it to my S13, Lancia Integrales, a 3dr Cosworth and we are currently fitting it to a turbo Hayabusa thats in a MK Indy. My 350 will be getting it at some point too. Comes with pretty much everything you'd want: launch control, anti-lag, closed loop knock, nitrous control (wet or dry) etc etc. Has a lot of nice safety features too - which are great if your engine is running close to the limit.
Haltech seems like a good plug and play choice - I've messed about with the software but not fitted to a car yet.