So you don't know what to do? Well, here's some tips from someone who feels your pain (and frustration!). Out of my 4 kitties (all boys), 2 of them like to 'express themselves' with their urine. There is nothing worse and more humiliating than sitting down on your couch before you realize it's been blessed. After reaching my breaking point and spending TONS of money on vet visits and products, i decided to put my techniques from years of working with developmentally challenged individuals into play.
So here's what you do, and it's going to take a lot of work and investigation:
1. IDENTIFY THE REASON
This is where all the time and work occurs. As you probably well know, there could be a THOUSAND reasons why kitty is doing this. What you need to do is narrow the problem down. First off, I suggest taking kitty to the vet for a check up to see if there's anything medically wrong. I'm going to assume that kitty is spayed or neutered (as any pet should be!), as unneutered male cats will spray around the house. Urinating around the house could be a sign of diabetes (especially if your kitty seems to be "leaking", rather than peeing and if kitty appears more lethargic than usual), or urinary tract infection, or anything really, plus 20 more diseases that humans can get.
If everything at the vets checks out, or if you'd rather investigate before going to the vet's office:
START A WORKSHEET - these are used in group homes and have proven to be quite effective. The idea behind these sheets is that the person (or in this case the kitty) is TRYING TO COMMUNICATE WITH YOU in the only way that she knows how.
So here goes, start the sheet out as follows:
A B C Record Sheet
A - Antecedent, or 'what happened right before they peed?' Any changes in the house, even minor? Visitors? Change in work times? Movement of furniture? etc. This could be a rather lengthy list until you start to notice a reoccurring pattern.
B - Behaviour, or 'what did kitty do?' Where did they pee? On what did they pee? Where did they pee? Was it right in front of you or did they try a sneak attack?
C - Consequence, or 'what did you do?' Did you scold them? Rub their nose in it? Ignore them? Clean the litter box?

Keep this chart going for a while until you notice a pattern. I've used them on my own kitties and eventually was able to identify that Jasper's picky about clothes left on the floor or untidy blankets on the couch as well as men in the home with deep voices (?), and Tiger is picky about my working overnight shifts, a less than clean litter box and overnight guests in general. This all took time to figure out, so please be patient with Kitty. And remember that they are trying to communicate something with you and don't know any other way of doing so.
Interesting side note: Humans will communicate with their bodily functions as well if they feel that they have no other means of doing so. For instance, in institutional settings (ie. jails and such), it is rather common for the acting out behaviour to involve feces when they feel that all other power has been stripped from them. Just be happy that you're not dealing with that!
2. Once you've Identified the Reason, CHANGE YOUR SURROUNDINGS.
If you've identified that kitty is urinating when you're not home for extended periods of time, play with them when you are home. It is more likely boredom than anything else. Create a kitty perch by one of your windows to keep them mentally stimulated while you're not home. Put a bird feeder right outside your window if possible. Leave the radio on when you go out, the sound of human voices is often comforting to a lonely cat.
If the reason is due to a full litter box, force yourself to clean it regularly. Some cats insist on it being cleaned up to 3 times a day. A lot of work, but much better than cleaning it off your couch!
3. CLEAN the urine spots well. Many cats don't like scented products and will urinate on top of them to cover it up. As well, cats like to pee on spots where they can smell that they've previously peed. I find that the only thing that works is diluted bleach. If you're worried about the colour in your fabric, either make it an extremely diluted amount, or use colour-safe bleach. I usually don't suggest chemicals, but seriously, this is the only cleaner that has ever worked in my home after spending sooo much money on other products. Beware of bleach though - keep them away from the area until it dries. As well, scrub the litter boxes with bleach and add new litter once dry.
An example of the ABC Record Sheet (Click to enlarge):

A few tips to remember:
Cats are not dogs. the Dog Whisperer techniques will not work on cats, as they are not pack animals. Do not try to show them who's boss, as it will likely lead to more acting out behaviour and possible aggression. Instead, as hard as it is when you're frustrated, try to look at their behaviour as communication, and then try to correct the situation as best as you can to make things easier on them.
Beware of some things your vet may 'offer' you. Like I said, I've spent thousands on trying to get Tiger to stop doing this (especially when it was a daily occurrence!). I've been sold the Felaway spray (which is supposed to mock feramone scent in cats and thereby make them feel relaxed). I sprayed it on my bed and within 10 minutes there was a fresh warm puddle, no joke! At $70 a bottle, you would hope that it would work better than that. I've also had Tiger on anti-depressants for an anxiety disorder (and yes, they make these for cats!). No result.
Cats do not like having their food near the litter box. Some are more sensitive to this than others. A Cat's sense of smell is stronger than a human's. How disgusted would you be eating in the same area that someone was taking a number 2?
Where they pee is just as important as the fact that they are peeing. Is it on the bed, on your side of the bed? This would obviously mean that the communication they are trying to make is with you and no one else; whereas if they peed on the couch in the living room, the communication is made to anyone who will listen.
And remember: YOU ARE ALL YOUR CAT HAS. You have your work, your friends, nights out, family, etc., but your cat has you and only you. This is the reason that any change in the house, regardless of how minor, can be so stressing on them. I try to remember it as this: I imagine if I woke up one day and my home was suddenly in Australia. Everything inside the house was the same, but as soon as i walked out that door everything was different. This would be the equivalent of something as simple as a furniture change to your cat; the world as they know it is suddenly turned upside down.
Your cat may, no matter what you do, still periodically urinate around the house. But if you identify the reason and take reasonable steps to correcting it, it will become less and less. My guys still do, but it's usually when I've been getting lazy about the litter box or use a new scented spray around the house. But I tell you - once every couple of months is much more tolerable than once a day like they were doing!
Let me know if these worked for you, or if you have any other suggestions, I'd love to hear them!
Good luck!