I, too, have cracked the screen of my G1 and am rather embarrassed to have made the same mistake so many times with touchscreen phones in the past six years.
In San Francisco, I have in the past had LCD/screen replacement done by "Kangaroo Mobile", which has a local site here. I contacted them about repairing the G1, and was told that to their knowledge, no one has yet begun to manufacture sell the requisite replacement parts (which according with HTC's development practices are not as common between similar/virtually-identical devices as one would hope) to set things aright.
I looked at the website of
http://pocketpctech.com , and they, too, seem yet to offer replacement for the G1.
The cost will be over $100 for parts and labor no matter where one goes. IIRC, the quote for HTC Tytn replacement by pocketpctech was quite high, at $150.
There will inevitably be a repair offering for this device, and I'm frankly quite surprised that the posters before me in this thread appear naive enough to cry "complete device replacement" where there it is so natural to expect that the thing can easily be fixed. I guess that's exciting, since those same people are likely to be new to handsets of this class and perhaps also new users of Linux. Bright side.
It looks as if we will have to wait for an off-brand provider of a matching LCD/touchscreen combination --but the only question is whether or not to buy a new device while waiting for a repair plan for the "old" one.