The J&L alloy headset cap weighs only 8g including bolt and features an extra light weight CNC machined top cap, with an aluminum M6 bolt, saving up to 10 grams over a generic alloy top cap with steel bolt. The cap itself is not much heavier than a carbon fiber top cap, much of the weight savings comes from replacing the steel bolt with an aluminum one which is 1/3 the weight. This bolt is non-structural, and only serves to lightly pre-load the headset before tightening the stem, and to keep the top cap on. The domed design looks generic, but it is available in multiple colors. At only $5, and saving 2g per dollar, it represents a good value, very low cost upgrade. It can be purchased on eBay.
Price: $5 [Very Low Cost]
Value: 2g/$ ($0.50/g) [Good Value]