Pictures would definitely help but there's no way to tell if they're simply some weird hybrid from cross pollination. Honestly, It's a shot in the dark as far as which types they are.

Here are some links to photos, sorry they are not the best! Let me know if the links do not work. 4 are round/oval like pumpkins, one is a peanut shape and the other seems to be a butternut squash. None have shown signs of being anything but green.

http://i1115.photobucket.com/albums/k559/dovesvspigeons/patch.png

(One of the many patches)

http://i1115.photobucket.com/albums/k559/dovesvspigeons/babymystery.png

(Baby starting to grow)

http://i1115.photobucket.com/albums/k559/dovesvspigeons/medium.png

(This one grew from that baby bud in about 2 weeks time)

http://i1115.photobucket.com/albums/k559/dovesvspigeons/littlemystery.png

(The white flowers are a different plant that the vine grew around, this one has stopped growing)

http://i1115.photobucket.com/albums/k559/dovesvspigeons/butternut.png

(What we assume is a butternut squash, also done)

http://i1115.photobucket.com/albums/k559/dovesvspigeons/mystery1.png

(The biggest one a week ago)

http://i1115.photobucket.com/albums/k559/dovesvspigeons/bigmyustery.png

(That same big one today)

Interesting.. how many types did you leave in the compost? Were they store bought or home grown? A few of those definitely look like probable butternuts. The others could be butternut hybrids if that's what went into the compost. There's no way to know for sure if they were store bought though.

Oh and the last one is pretty general in its shape so it could be almost anything. Kinda need to wait and see how it matures. At the very least it has the potential to be a good carving pumpkin for halloween.

Ya know, we compost absolutely everything are a plant-based diet kind of family so I'm not sure what could be out there--anything and everything, really. It's just amazing how HUGE the three have gotten, figured they were going to your regular orange pumpkins considering the size!

Everything is store bought, we only grew eggplant, strawberries and tomatoes this year. And they were in their own garden far from these patches. Like I said, it seemed to happen after we released a rehabbed squirrel so he could've grabbed anything from the compost..it is quite neat to watch. This is new for us so we're not sure when to cut them from the vine etc...

Awesome, will keep an eye on these. None are showing any orange, strictly dark greens so far, so I'll keep waiting. The vines seems to be turning yellow so we weren't sure if we should keep them on the vine/if they were done or not. We have no clue what to do with these plants as we've never had them before. Thanks for your info!

Let the stay on the vine.. Winter squash will ripen as the vine dies back in most climates. The stem should become woody and you can use the fingernail test (try to push one in.. it'll resist a lot when it's ripe).

Looks like most are zucchini for green skin x orange pumpkin for size and ribs. Both are Cucurbita pepo and cross if allowed.

If my hypothesis is correct zucchini will impart rather bland flesh to the result. Nevertheless quite useful stuffed and roasted. Some pepo hybrids eventually are very bitter, inedible so taste a small piece before cooking.