As the resident Christmas Ornament collector junkie (my family and myself have been collecting since I was a tot. A normal Christmas season for us involves around a dozen different trees in every room of the house), I'll answer your questions.
Hallmark has its ornament premiere every year in July. Most of their ornaments come out at this time, but there are additions that come out various times up until Thanksgiving. Hallmark has not had a Muppet Christmas ornament for ages. It wouldn't surprise me though to see one pop up in next year's line of ornaments if the new show makes it to television next year. I was also surprised that they did not have a 25th anniversary ornament this year, as Henson and Hallmark have had a long relationship. I have also longed for a Muppets series, much like their Dr. Suess and multiple Peanuts lines over the years.
To check out this years line of ornaments use this link:
Hallmark 2002 Online Dream Book
Now, Carlton Cards also has their line of ornaments out for 2002. They haven't had many Muppet ornaments over the years, but recently they have had at least two Sesame Street ornaments per year. This year they have Cookie Monster and Elmo. Carlton ornaments aren't that popular with a lot of collectors, and oftentimes you can find previous years ornaments on sale alongside the current years line.
Here's the link to this years line up:
Carlton 2002 Ornament Line
There have been other Christmas Ornament companies to feature the Muppets as well. Midwest of Cannon Falls made some great resin ornaments, and Christopher Radko had some interesting blown glass ornaments as well.
There have also been reports that the Bradford Exchange (or Franklin Mint, I can't remember which) was going to release a series of Muppet ornaments, but it looks like that fell by the wayside.
Grolier also released some wonderful Sesame Street Ornaments in the 90's.
Phil has most of the Muppet Christmas Ornaments in his collectibles section. Once Halloween is over I will dig out some of the ornaments my folks brought me on my last trip to see if I have anything that is not included in the listing.
Hope this was of some help!