This new SDHC memory card from Toshiba has a write speed of 6MB/s but it's quite expensive.
According to Toshiba it will be launched for $699. The high price makes this card kind unattractive tough, considering you can get a 4GB SDHC memory card for about $40.
If you don't mind swapping memory cards every once in a while it's much cheaper to buy a couple of 4GB SD cards and save almost $300.