AEM TRU-Boost for most accurate Reading and Controller. The only downside i have to say about it (on my 03 Evo) is that you have to calculate boost by percentage % and not by psi. So you have to adjust and figure after running your car.

Awesome boost gauge and controller once you get the hang of it. Hallman's are good too.

Fairly simple to install because it comes with very detailed instructions.