HDGuru published what is most likely the first review of the Pioneer Blu-ray player BDP-HD1. HDGuru actually finds many similarities between the Sony BDP-S1 and the Pioneer BDP-HD1, which leads to the conclusion that they are both made by Pioneer.

Quote from the review:
"Commencing set-up made clear that there were more similarities between the BDP-HD1 and Sony’s BDP-S1 than just the rear panel, as the two share identical on-screen instruction graphics, looks, placement and some fonts. The open drawer revealed the two players use the same disc drive as well, leading me to ask a Pioneer representative who builds its player.
I was assured that Pioneer builds its player, including the drive, which makes it clear that Pioneer also builds Sony’s player. "
Read the full review.

Like the Sony BDP-S1 the BDP-HD1 was delayed as well and is supposed to ship still end of 2006.
The Sony BDP-S1 ships now from Amazon.com for $979.

Other Blu-ray player choices are:
Samsung BD-P1000
Philips BDP9000
Panasonic DMP-BD10