Tire Recommendations?
 

Need 2 new rear tires for 2008 350Z coupe; any recommendations?

round black ones.....

^^^^ solid advice. 2nd.

Dont mix and match tyres, it's a daft idea unless you're drifting the thing constantly.
Depending on your sizes (which you've not said), for an all around great tyre Michelin PS4, but get the fronts as well.

Currently have Ventus brand, 245/45R18 rear, and 225/45R18 on front; only rear need replacing. Looking at Coopers, but sounds like you would suggest more Ventus, unless I am replacing all 4?

IF you drive hard, street/track then I'd stick with the same tyre/model on all corners.
If you're just driving around a city and take it easy, it probably doesn't matter.

the hankook ventus imho are crap, when i had the nissan i had the bfg sport comp 2's and liked em, on the vette i had the ps4's loved em. and on the cadi i have continential extreme contact, so far i like them