For anybody who complains that Sony's Memory Stick Duo memory cards are too expensive compared with other forms of flash memory, DealExtreme has a solution. It's the StarJade SDHC microSD to Memory Stick MS Pro Duo Adapter Sleeve, which retails for a mere $2.85, including free shipping. Unfortunately, the only problem is that it's illegal (see "update" note at the bottom of the post).
A quick comparison on Amazon for prices of microSD and Memory Stick Duo reveals that an 8GB microSDHC card costs around $20 (with shipping), while an 8GB Memory Stick Duo card comes in around $34 with shipping. (Yes, the adapter supports higher-capacity SDHC microSD cards). Step up to a 16GB card and the delta is about $25, with entry-level 16GB microSDHC cards retailing for around $50.
The description on the product page says the adapter works with a wide variety of portable electronics devices, including cameras and audio players. We can't vouch for the reliability of the adapter but we did order a couple to test out, which we now realize may have been a no-no.
Note: This adapter won't work with the new PSP Go, which uses Sony's Memory Stick Micro (M2).
Update: Mike McCarthy of SanDisk writes: "The microSD-Memory Stick adapter is illegal, unlicensed and infringes on Sony Corp patents. Maybe it's cool to promote this stuff as a 20-year-old blogger, but I thought CNET would have higher standards." As a result of Mike's comment, we have summoned some maturity and edited the post.