Although it's not getting much attention, rumors of US casuaties are starting to be confirmed on this webpage, with 18 listed so far. Only two of the 18 listed casualties are reported as having died in the past 72 hours, however, indicating a significant delay in reporting due in part to the need to contact the next of kin. In the past 72 hours, there have been reports of numerous US military casualties that have yet to be officially reported.
Britain, however, seems to be confirming casualties in a much more prompt manner than the US, usually within a day. This could be due to their method of reporting casualties -- they may be reporting soldiers who have died, but not revealing names until the next of kin are notified. According to this article, confirmed British casualties in the war are now at 20.