If we're talking artistic preferences, any number of possibilities exist if a story depicted one found in an ancient extraterrestrial tomb or crashed to Earth and emerging from the corpse of an inhuman pilot. I'd be interested to see one with an extra pair of arms, for instance. And there was a fairly good Photoshop someone did of an Alien torso on the Spider Gremlin's body, from 'Gremlins 2', which looked suitably horrific and biomechanical.
In terms of Earth creatures, a crocodile or tiger one could be interesting. Something to give reason for the jaws and teeth to have more sharpness and/or emphasis.
I know the comics depicted a crocodile/alligator one, but it seemed oddly bulky and heaven knows why the tail was so strangely massive. Seemed an odd choice of change, considering they left the jaws at exactly the same size as normal.
I like the designs which emphasise viciousness and predatory brutality, but a lot of artists draw them looking decorative, instead. Like the Kenner toys.
Incidentally, I long to see the superfacehugger on screen, some day... Aside from the leg membranes (they seemed too at odds with the rest of it), it was an excellent design.
I've made some interesting Alien designs in 'Spore', but the limb/object number limitations don't let me get as creative as I'd like to with them.