Intake Manifold
There are many advantages to swapping intake manifolds. Lighter weight and better airflow into the cylinder heads are certainly chief among them. Of course, this is another piece that must be matched to the rest of your combo. Displacement, cam and head selection, and planned rpm range are all factors to consider. In fact, these parts are so dependent on one another that companies like Edelbrock like to sell manifolds as a "Power Package" with a cam, heads, and even a carb. That being said, you can look for power gains of 20-30 hp with a wise manifold selection, and prices start as low as $100.
Underdrive Pulleys
OK, we know these kinds of things usually come in 10s, but what can we say? We came up with 11. Underdrive pulleys are a relatively quick and easy way to free up some horsepower. March Performance tells us their Performance Series kits usually increase power about 12 hp. The Power & Amp Series pick things up by 10 or 11 ponies and allay fears about inadequate charging by spinning the alternator faster. A pulley kit starts at about $150, while full serpentine conversion kits are about double that.