Check out Art Text by BeLight Software. It lets you create glassy buttons, stylized text, and icons in different styles. MacUpdate Promo happens to be running a 30% discount on it till the end of the week.
There is also Aquatint, but it requires that Rosetta be installed before you can run it on Intel-based Macs. It's really old.
A favorite of mine (though it doesn't manipulate text like Art Text) is PhotoStyler. It lets you create all sorts of effects. It's perfect for the Photoshop-challenged, like me. The publisher, Corner-A, also makes other apps that you might find helpful.
And last but not least, check out Apple's list of Imaging & 3D apps.