Samsung, LG and Motorola are all known to be working on Android Phones. We know that Motorola's is some type of "Social Networking" phone but the other two are still a mystery. Don't rule out HTC making a second Android Phone before another manufacturer makes their first.
I think part of it comes down to the carriers. Verizon and AT&T aren't all that anxious to jump on the Android bandwagon and Sprint is waiting until their 4G WiMax network has more coverage so their first Android Phone can be WiMax capable.
Thats the American market though... abroad is somewhat of a mystery to me as I'm not as familiar with the mobile landscape.
There are some SMALLER manufacturers who will likely have devices out, most recently... Hop-on announced they would have an Android Phone in January. Others reported this as "Android Phone News" while I took a more skeptical approach on Phandroid (
read here)
I wouldn't plan on T-Mobile releasing another Android Phone to cannablize the G1 but who knows... we've seen crazier things before.
This all being said its kind of an odd waiting game where the stars of manufacturer/carrier have to align perfectly and who knows exactly when that will happen. But... by the end of Q1 2009 we should have SOME new Android Phone and when the 2nd comes... i think the 3rd, 4th, etc... won't be far behind.