Those Stirrings bitters are really good - but they're non alcoholic (?!?) so if you do procure those be sure to refrigerate (and/or toss a splash of spirits in them).
The Fee's Peach & WI Orange are great - the Lemon & Grapefruit are so so (too sweet/potable).
There are a few other odd bitters - check out
The Bitter Truth or the Hermes line of products by Suntory (I don't think they have a website) are available from
here.
There are some other ones out there also & you could always have a go at making your own.
Tiare's Grapefruit Bitters
My Spiced Lemon Bitters