Just for the heck of it, in rough order of preference:

1) Quaife LSD - Once I got used the the feel of real traction, hard to imagine life before it. Sticky is good! Lotsa fun in the rain

2) Y-pipe. Gotta love the power.

3) STB's - Front and rear, both together as a set. Include the RSB and the Maxima starts to feel like a real sports sedan. I'd also include the polyurethane bushings for a tighter feel ...

4) Adjustable struts. Nothing beats suspension tuning, IMHO. How else you gonna enjoy the power mods?

5) Performance clutch and flywheel. I did them together, so I'm putting this as a set. Faster revs, heel/toe shifts, and together with the clutch a lot more power on the ground. Mod #1 makes more sense after this!

6) Cone intakes. I've tried a couple; they all sounded great. Put the stock intake back for smog check, didn't mind it much, though.

7) 235/45zr17 tire/wheels. Lower profile sidewalls really carve the turns, and I love the bigger contact patch. Look great too, and it's amazing what selective tire pressure can do for performance tuning ...

8) Coilovers. Linear springs are amazing for performance driving; carving foothills, backroads or autocrossing, they can't be beat. Steering is so tight! On the other hand, they're rough on urban freeways. An acquired taste, I guess.