I'm trying to decide among these cars. Any help will be appreciated.
Below are my thoughts so far (after test driving all three at least
twice). Any other cards I should consider?

All three I'm only considering only in manual transmission.

(1) I really like the power and tight suspension of the G35, but
dislike it's fit and finish (looks cheap, buttons and knobs are a
little tacky, and the headliner is the same cheap one as the one on my
Grand Am rental). Also, the stereo isn't good either, I'm not
impressed with the "Bose" system, and I'm not sure if I could easily
replace it without the interior looking even worse, speakers fitting
poorly or some other problem. When you turn it up (and I don't mean so
that you can't hear people talk) it starts to sound bad (noticeable
distortion) quickly.

(2) The Audi 3.0 Quatro seems like a nice compromise. I give up a
significant bit of power and some of the tight suspension (even on the
sports package), but the fit and finish is the best of the three, the
stereo is really good, and I gain the all-wheel drive. It feels solid,
it sounds good, it drives really well, and I'd feel really safe in it.
I'm upset it doesn't have a real NAV system yet.

(3) So far I've only test driven the xi (see note below). I expected
to be impressed and I was really disappointed (as compared to the
Infinity). The BMI is also pricey, but maybe I'll decide it's worth
it. I don't want to actually pay much over $35k (after dealing), but
then the i will be cheaper than the xi anyway, if I decide to go with
it. Still, it appears they're becoming hard to find (they've stopped
making them and the next ones come out May-July). I'm still not sure
why people say that the 330 ride (well, I'm actually still thinking of
the xi ride, since I haven't driven an i yet) is better than the G35
because it seems softer. It definitely rocks more on turns and if you
just jerk the car to the left and right quickly. The steering also
isn't as tight as the G35. I wonder if people just like a softer ride
than I do. It would be helpful to hear someone even just say, "Yeah,
you seem to like a tighter ride than I do. I like the luxuary ride v.
sports ride balance of the 330, but I realize I don't feel the road as
much as in a G35." I like to feel the road because it gives me
confidence I know just how the car is reacting to the road. I also
like good feedback in the steering wheel. I also like a little more
power than the 330 has.

One further complication--NAV:
I also would really like a factory navagation system. Audi won't have
one until May (I'd consider waiting, but my last car was totalled--not
my fault--and I don't know of a good short-term solution to just
renting a car each week. Anyone know of a good way to rent a car for 5
months?).
I haven't seen BMW's NAV system yet, but I fear that will make it even
harder to find a 330.
Infinity already has a reasonably nice NAV system.
(Note: I really liked the Acura TL's NAV system, but the ride is way
too soft for my taste.)

My dream would be the G35 engine and feel with Audi fit and finish with
the Acura NAV system.

I wondered if there might be a difference between the xi and i on
handling. The Audi salesman I spoke with seemed very knowledgeable and
was willing to discuss my understanding of the 330xi versus the G35
(and didn't even seem to mind we weren't talking about the Audi and
that I might have written it off). He said he thought the xi might
drive differently and suggested I drive an i. When I mentioned it to
the BMW dealer over the phone, he told me point blank that I was wrong,
that he knows the cars very well and they drive exactly the same. I'll
have to drive one.

Thanks for your advice,

Rick