Caterpillar ID

[Linda & Jeff Ives]

I found a caterpillar in my garden today resting on the stem of Wood Aster,
and I'm having difficulty identifying it.  I've checked out the Discover
Life site:  http://stri.discoverlife.org/mp/20q?guide=Caterpillars
with no luck.  I let a friend borrow my ID books, and I haven't found
another site through Google.  I'd appreciate any suggestions for good
websites with photos of caterpillars. 

Some notes: I had a Monarch laying eggs in my garden today, (Monarch Way
Station #96, I think!).  I've had my garden of Milkweed and nectar plants
for years and NEVER found an egg or larvae.  My garden is filled with
Monarch predators that have always beat me to the eggs , I guess.  
Last week I had a Great Spangled Frit patrol the garden for 2 days, not
letting any other winged creature near.  I even saw it chase a bee away. 

Thank you!

Linda Ives
Marlborough, CT