I have been slowly building up my pattern collection. So far I have:

Project Puppet
Glorified Sock Puppet
Pinhead

One Way Street
People Puppet
Musical Note
Sun (from their "Let There Be Blacklight" book)

Puppetpatterns.com
9 Full body, moving mouth puppets
   (People, Cow, Reindeer, Donkey, Camel, Lion, Dog, ,Sheep, Duck)
6 Full body, stuffed head hand puppets
   (People, Cats, Mice, Bunnies, Pigs, Cows)
3 Easy hand puppets
   (People, Elephant, Horse)
2 Finger puppets
   (People, fox)

Backes Puppeteers
Easy puppet pattern set
   (Alligator, Bear, Bird, Cat, Chicken, Dog, Dragon, Elephant, Mouse, Rabbit)

McCall's Crafts
Sesame Street characters
   #8525 (Prairie Dawn, Bert, Ernie, Grover)
   #8527 (Oscar, Big Bird, Herry Monster, Cookie Monster)

Miscellaneous
Blue boy pattern

I don't tend to follow a pattern precisely, but they are nice to have as a starting point.

Any suggestions for patterns I should check out or keep an eye out for on eBay?

Well, this is a question I can't just answer for you. It's one that depends on the look of puppets you want, how much you want to spend, etc.
I'd say the Project puppets ones are the most versatile.
Some of the One Way Street patterns are currently on sale, and could be useful as a base too.
But if you can get the McCall's ones, that's the one(s) I'd go for.

But if you can get the McCall's ones, that's the one(s) I'd go for.

Do they have other ones besides the two packets I have?

I guess that is really what I am asking about, what patterns are out there that I might not know about yet. I do have a pretty good concept of what I might find useful, but that doesn't help much if I have never heard of them.

Ooops. I must have been half asleep. I thought you were asking which of the patterns listed you should get.