Obis

I own an obi, but i'm not sure if it's the obi that creates a design on the back. It isn't very wide, perhaps half the width of other obis, yet it still is stiff enough to make me think it's one of the most outside obis. Does anyone know what I'm talking about? Do you know if it's an Obi, or a variation of an Obi?

There is a type of obi that is called "han-haba obi" (literally "half width obi"), which is about 15cm wide or so... used for more casual occasions, polyester ones used with "yukata" or wool kimono, Hakata obi used with yukata, wool kimono, Komon kimono, etc.
You can do a lot of different knots and ties; for photos:
http://www.geocities.jp/cocon_yu_mo/hanhabairoiro.html

So shopping for new obis, i recently bought a white, silk furisode from ichiroya.com. It has the cart motif on it. In any case, I was searching for appropriate obis to go with it, can you explain the different kinds?
Fukuro
Heko
Maru
Nagoya
Tsuke

I'm not too familiar with the different styles, but I know that since "furisode," being the best formal kimono for unmarried women, are quite fancy, the "obi" should be equally fancy - meaning, take "fukuro obi" or "maru obi," but "maru obi" is not often seen lately, that you should go with "fukuro obi."

are maru obis out of fashion?

"fukuro obi" - full width obi made by sewing top/outer cloth (with pattern) with inner cloth (without pattern) together.
"maru obi" - full width obi made by folding a double-width outer cloth (with pattern) in half and sewing the side. So it's full patterned inside and out. It's just that they do not seem to make any "maru obi" anymore - probably due to higher cost and heavier weight (you have double the full patterned cloth). Nowadays rarely used, only for the bride's kimono IF ever at all.

so if i were to buy a maru obi (i'm assuming an antique) would i be old fashioned or would it matter at all?

It's simply, just not used - people (who are familiar with the "kimono" way) might take it apart to make a fukuro obi out of one, but IF EVER they are used for bride's kimono or stage dress kimono only. It's not matter of whether you will look old-fashioned or not - people just don't wear it.
Also note that it will be extremely heavy and difficult to tie....

Just to reinforce AK...

Since Maru Obi is so heavy and thick to handle, many people have it reformed into Fukuro Obi.
If you plan to buy Obi for Furisode, I also recommend Fukuro Obi.

Nagoya Obi is too casual for Furisode. Tsuke Obi is pre-tied obi so as to save time and you can ask Kimono tailor to have your obi made into Tsuke Obi. Heko Obi is a very simple (soft) obi for boys/children.