So my car is plenty stiff and holds corners great. But being a Honda v6, the engine is not terribly immediate. I'd love to have the engine climb the revs faster and just feel more involved in the car.

SO: Throttle Booster or Underdrive/Lightened Pulley?

I'll probably end up doing both, but which one is most noticeable?

Forced induction or spray it !!!

What's a throttle booster?

Blower. Underdrive pulleys will be a waste in that car.

Is your car manual or automatic?

Do you autocross or track it? I put a polyurethane insert into the front engine mount on my Neon and it helped alot for autocross. Stopped wheel hop on the starts and keeps the engine from flopping around every time you are on and off the gas.
It does make idling a little rougher but it might not be bad with a v6.

I do go to the track occasionally. I find that the biggest thrills are to be had with an engine that spools up quickly, and delivers itself immediately.

A throttle booster basically amplifies the drive by wire throttle signal, so the throttle response is faster. It's much easier to understand if you google it.

Why wouldn't I see any improvement in engine response from a lightweight pulley?

I am going to assume that, being an Accord, this is a modified street car aka "daily driver". While I was never much into the Honda scene (except for S2K and NSX), I know a lot of people who autocross stripped down Integras and Civics with K-series or other drivetrain swaps.

I personally think you need to stay away from ANY kind of forced induction including Nitrous until you have a proper suspension, brake, and wheel/tire setup or you are not only wasting money, you are endangering yourself.

That said, I think the following will net you the best gains for bolt ons:
- Ceramic Coated Equal Length Headers
- 200cell Hi-Flow Metallic Cat OR Test Pipe (cat delete)
- Underdrive Pulleys
- Lightweight Flywheel and Clutch Assembly
- Cosworth Intake Manifold (or similar)
- Camshafts
- Lightweight 17x8 up to 18x9 wheels all around (a square setup; D-Force makes 17s that weigh about 16lbs per wheel...), help with acceleration, braking, and handling

I do not know what kind of intake yours is, but it is very much worthwhile to go with a full cold air intake that puts the filter outside of the engine bay and replaces every bit of OEM intake ducting with a 1 or 2 piece unit featuring smooth bends, a heat shield, made from plastic or Carbon Fiber, and wrapped in heat resistant "cloth" or foil. Otherwise, you are losing power.
It does not have to cost a lot either... Since it will be covered, you can use the Spectre Build Your Own intake parts from AAP/AZ/OReilley/Peps/etc. Use silicone gaskets between pieces, minimize length while still getting the filter (afe ProDry cone, ideally) into the bumper. Paint the tubing with High-Heat-Resistant paint after sanding it, then wrap with inexpensive DEI exhaust wrap, followed by a wrapping of aluminum tape to act as a radiant barrier.
Total cost is well under $100 since you already have a cone filter.

In the end, though, you will get much, much more fun out of a car with a properly sorted high quality suspension than a bunch of bolt on engine mods...

Wow thank you so much for the extensive and informative response!

I think you're right about suspension being the key to a fun car. It's on tight lowering springs and the car just feels heavy. It definitely has no lack of grip, but some quickness (and comfort for that matter) would be nice. I'm not sure if that means upgrading the shocks to Koni Yellows or something, but I would like to hear what you have to say on the matter. Do you think Koni yellows would solve that?

I think the whole thing behind the under drive pulley/ throttle booster is to make the car feel lighter and more nimble.

Also, a cat delete can be gotten for $80. I have an intake and exhaust, so do you think that is more worthwhile than a pulley?

Personally, I have tried all the various types of aftermarket setups, and I will never go with anything less than at least damping adjustable coilovers. A cat delete will not do a lot on its own, as you need a tune to really take advantage of it, and the exhaust manifold then remains a huge restriction. I am sure you could get a set of ceramic headers for under $3-400...and that would solve both flow issues. Another issue is weight... You would not believe what removing 100lbs can do. It is not earth shattering, but it is free.
Pulleys, if good quality, will make your car more responsive due to lessened parasitic loss. In the BMW world, $200 gets forged aluminum pulleys that are 40% lighter and decrease drag 33%. When my car was still naturally aspirated, I saw a peak 9whp from high end pulleys (alternator, water pump, power steering). Later, a 50% lighter crank pulley and Stewart water pump bumped that up a bit. Throttle response was better, and it is one engine mod that gives a steady power rise across the RPM range with no power loss.
I think it is a good place to go from where you are at, as you are gaining back power that you already have instead of trying to force the engine to produce more.

i would completely ignore a plug-in throttle booster. it's an inline device that adds complexity to a critical system. You'd be much better off retuning the ECU.

Exhaust Headers, #1 gain
Intake, #2 gain
Lightened flywheel (helps acceleration but not top-end) - snappier response/acceleration but takes some work

If you re-tune, you can advance the timing for more power and run a higher octane fuel to prevent detonation... raises your operating cost but it's cheap power.

An underdrive pulley is a good relatively cheap mod.
Figure 5-6 HP'free' at 6k RPM.
If you have a restrictive snorkel on the intake [for sound attenuation] , open it up. Ambient air ['cold' air] intakes are best for all but extreme winter conditions [not hot under hood air].
Electronic tuning/chip is great - this is one thing to be highly considered!.
Sure , you can do all sorts of mods for BIG money and time, but these things will net you a lot of improvement, without being financial deal killers.

I'll look into tuning... jet chips has a full ECU tuning for like 400. What do you think about that? As opposed to an under drive pulley...

Still waiting.

^^^That's an excellent question.

IME the underdrive pulley(s) are a nice upgrade for many cars. Seems to me the smaller the displacement the larger the difference. But as Doodfood is trying to ask, the transmission has a great deal to do with what will work best for you.

Tuning is almost always great. But every platform has vastly different strategies. For instance, a Jet chip will not do squat for my car due to the adaptives quickly negating its effects. You may need a complete reprogramming. One of the Honda experts can fix you up there.