What household products neutralize cat urine odor in carpet?

Well, I found that oxyclean and frebreeze works well.
References :

Baking Soda – cleans, deodorizes, softens water, scours.
Soap – unscented soap in liquid form, flakes, powders or bars is biodegradable and will clean just about anything. Avoid using soaps which contain petroleum distillates.
Lemon – one of the strongest food-acids, effective against most household bacteria.
Borax – (sodium borate) cleans, deodorizes, disinfects, softens water, cleans wallpaper, painted walls and floors.
White Vinegar – cuts grease, removes mildew, odors, some stains and wax build-up.
Washing Soda – or SAL Soda is sodium carbonate decahydrate, a mineral. Washing soda cuts grease, removes stains, softens water, cleans wall, tiles, sinks and tubs. Use care, as washing soda can irritate mucous membranes. Do not use on aluminum.
Cornstarch – can be used to clean windows, polish furniture, shampoo carpets and rugs.
Citrus Solvent – cleans paint brushes, oil and grease, some stains. (Citrus solvent may cause skin, lung or eye irritations for people with multiple chemical sensitivities.)

Best of luck!
References :

Natures Miracle! You can find it at most pet stores. It is an enzyme cleaner (basically eats up bio matter).

Here is there web sight but if you say it at a pet store they will know exactly what it is because it is the best.

http://www.naturemakesitwork.com/home/index.php

I have to say that some of the other suggestions may actually bleach parts of your carpet so be careful.
References :
Worked at a veterinary clinic where it was the only cleaning product we sold.

ODOBAN……you can purchase a small spray bottle of it from a few grocery retailers and select Walmart stores. That way you can try it first without spending a boatload of money. The spray bottle is about $2.75. Odoban has been around for quite some time and it effectively breaks down the components creating the smell.
A one gallon jug can be found at Sams Club if you like it. It’s $10 and when mixed to "pet strength" with water, it yields 32 gallons of product.
It’s not just good for pet odors. It’ll take the smell out of d*mn near anything. I use it faithfully in my shampooer when I clean my area rugs. It’s also good for the laundry. It’s a disinfectant as well.
I honestly can’t think of anything "household" to tell you to use that’s effective. I’ve had cats my entire adult life and I’ve tried it all at one time or another. This is the ONLY thing I’ve ever tried that truly worked.
Besides that, your problem is most likely below the carpet level, in the padding and possibly into the sub floor. If you stand any chance of getting that smell up you’re going to have to soak that carpet like mad and anything you use will be expensive because to eliminate the problem completely you’re going to need a ton of those designer sprays.
ODOBAN…try it, you’ll be glad you did. That $2.75 spray bottle in the carpet cleaner should be enough to get you going. That may not cure it all together but I guarantee you you’ll see a big difference.
References :
http://www.odoban.com/