The Mad Rock Ultra-Light Straight is the best deal for a lightweight carabiner we found. It's hard to find any cheaper carabiner, let alone a really light one. Its forged I-beam construction makes it pretty easy to hold and overall it was a solid but not exceptional performer.
For the low price of $6 this is one of the least expensive, lightest and strongest small to medium sized carabiners on the market. It is very similar to the Wild Country Astro except it is just a gram heavier (30g vs 29g for the Astro). However, it is $2 cheaper than the Astro and $2-3 cheaper than the other top biners in its category: Black Diamond Oz Carabiner. Overall, unless you want the absolute lightest carabiners (which are also tiny) like the Metolius FS Mini or CAMP Nano 22 Carabiner, it's hard to go wrong with loading up on Mad Rock Ultra-Light. It's the best wiregate carabiner for the money.