I'm assuming you have a V6? On the intake side, many go with the Volant intake system. It's a pretty good system and last time I priced one it was around $245 from THMotorsports. On my 06 Pathy, I went with the aFe Momentum air intake system with the dry filter. I really like it a lot, but it is expensive at around $465. Keep in mind that some people have had installation problems in their vehicles resulting from the top mount location, which is part of the ABS actuator bracket. If you do, adjust the bracket down to lower the mount point and it will fit fine. I also installed an XTP plenum spacer, which puts a little more power in the mid-range and is a worth while investment. Don't bother with throttle body spacers as they do nothing for an engine with multi-port fuel injection.
The exhaust will depend on how much you want to spend, how much work you want to do and what is your tolerance for "drone." If you don't want to listen to the "drone," you are best to leave it alone. A lot of people have installed the Gibson cat-back systems, which is good. On my Pathy, I replaced the stock exhaust manifolds and post catalytic converters with Doug Thorley shortie headers and mid-pipes. I then cut out the factory main muffler and installed a Magnaflow 12580 muffler, which is very close in size to the factory muffler but a straight through flow design. This will require some custom pipe work as the 12580 is a 2-in/1-out configuration compared to the single in and out configuration of the factory muffler. It's a simple job that any custom exhaust shop should be able to handle. I should note that at first, it doesn't sound great, but that changes as the muffler breaks-in with a few hundred miles on it. Mine took about a thousand miles before it was finally done with the break-in stage and it sounds great (to me, anyway) now, especially in the 2000-4500 RPM range. I noticed a modest increase in power after all this, but the biggest difference was noticed after installing a performance tune using a Superchips Flashpaq tuner. The 87 performance tune was good, but I now run the 93 octane tune with 3 degrees timing advance and the rev limiter and speed limiter raised. If you are not going to install get a tuner, be it Superchips, Bully Dog, Hypertech or Up-Rev, I think you may be disappointed with the performance results of the upgrades, unless all you are looking for is to make it sound louder.