Yep. Apparently so, it's even possible for GC's and Sun's to hybridize! I'm still waiting for a photo of one!
Of course, I've even come across a cockatiel/galah hybrid, conure/macaw hybrids, even a princess parrot/scarlet chested parrot?parakeet? hybrid.
Here's some photos, and if you'd like I can find more information about the birds (since I didn't save the sites they came from)
http://smg.photobucket.com/albums/0903/ ... s/Hybrids/
However, please do note, that hybridization is frowned upon by many, and generally speaking it's not a good idea to hybridize them, thus to keep their lines pure.