You could put in some pillar candles, and decorate for the various holidays.

But if your cats are used to playing in there, don't light the candles. :O

Thanks mama for the suggestion...I was actually thinking of doing that around Christmas time but am at a loss as what to do with it the rest of the year!

These are candle inserts that are similar to what I used in a bedroom fireplace that was not opertional.

http://www.ironaccents.com/inserts.html

and

http://candlesbyconnie.com/fireplace_candle_holders.html

Your other option is the Gel Fuel

http://www.realflame.com/

justducky, It's officially Fall--get some pumpkins or gourds--good 'til Christmas decor is unpacked.

Then after Christmas, if you have a New Year's celebration, use some silver or gold tinsel (Your cats will LOVE IT!)

And, let's hope that by Easter, you'll have a new, completely functional fireplace--you can celebrate the Equinox with a fire!!

A definite NO NO NO to tinsel!!

Yes, cats love to play with it, but it can easily be swallowed and kill them! I won't have it in my house at all since I have two cats. They love playing with ornaments on the tree, which is okay, but tinsel--never!

They make electric log inserts, some that are just decorative with flickering light and crackling sounds, or log inserts that produce heat and have a fan but don't need to be vented. Or just having a grate and real logs stacked would make it look like a working fireplace, and you'd be able to use them when it actually is!

Here is a link that might be useful: Electric logs

Tinsel is very dangerous. Some cats will play with it and not eat it, but if a cat does start swallowing something long and thin...they cannot cough it up. They keep swallowing until it's gone and the metal tinsel will cut up their stomachs.

You're very fortunate to have a fireplace, even if it doesn't quite work, just yet. It's still a great focal point and gives you a wonderful place to hang stockings :)

Thanks everyone! Yes, tinsel is a no, no. I do like the "harvest" idea and I am looking into the "fake logs" right now. I love the way it looks at christmas time with the decorations and stockings on the mantel so I was trying to get ideas of what to do with it the rest of the year so it will look just as good. Thanks to everyone for the suggestions. I will try and post a few pics once I get it set up!

Large green plants like ferns work well in fireplaces. If you don't have luck with the real thing some of the fakes can look VERY real.
Another idea is a large flower arrangements. Silk flowers done in a lovely vase and set just in front of the fireplace opening can fill the space. The cost can hurt UNLESS you are smart and buy on sale over a period of time!

OOPS--apologies to cats and cat owners everywhere! I had no idea cats would eat tinsel!

Mama goose- I know, my mom always had tinsel and never had a problem...until one of her new cats decided to start eating it! After that...no more tinsel, but she does have the little plastic/crystal icicles and they are very cute with the Christmas tree lights :)

Thanks, lavender_lass. I thought of suggesting a nice houseplant, but my sister's cats chew on them, so that isn't a good idea.

justducky, do you have any crocks or stone jars? Several of those would look good, if they match your decorating style.

Oh, and the Christmas lights just gave me an idea--you could loop the tiny white lights around your arrangement, and turn them on at night, unless...I just had an image of Chevy Chase's CHRISTMAS VACATION--cat + Christmas lights...nevermind.

Mama, I was thinking of the christmas lights too...until I got the visual of a crispy kitty in my head. So basically nothing hanging, dangling or swinging around in there! The problem I am having is finding something big enough to fill the space because it is so large. Maybe an arrangement of candles w/taller holders (not lighting them of course).

I once made a fireplace screen with a piece of plywood and some left-over floor paint. I stenciled designs to coordinate with the Batchelder-type tiles on the surround. If you don't paint or stencil, you could decoupage, or use scrapbooking items to decorate the front. You could also make it reversible by painting a Christmas scene, or, again, decoupage saved Christmas cards, on one side.

I'm linking to the e.how site with instructions for making several types of fireplace screens. I like the old shutter idea. Of course, you could go buy one, but what fun would that be? :D

Here is a link that might be useful: e.how fireplace screen

we just purchased a home with four non-working fireplaces. so i have been collecting inspiration for decorating fireplace holes. here are a few pictures i've found.

If it is a wood burning fireplace it needs a "chimney" independent of any existing gas vents.

If it is a gas fireplace it would need whatever "vent" was required by the manufacturer's installation instructions.

LOL, when I look at the blue FP, all I can think of is 'Fahrenheit 451'!!