I have tried a carpet spot cleaner from Clean Freak that worked very well for us on several different type stains. It is called Spot Care II. The can is designed to hold upside down and has a stem that you push sideways to activate the spray. It can be used while standing up. I really like that part. I can hang a can on my side and while using the wand I can simply grab the can and spray while holding the wand and not having to put the wand down and bend over. www.cleanfreak.com/Qstore/c000034.htm
The product worked really well on most general stains but it is not for every stain. I have never found a product that works on all stains. You should have a good selection of products with you in you bag . Never give up on a stain after only trying one stain remover. I usually have a minimum of 6 spot cleaners with me. What works well on one spot may not on another. Examples of spot removers, Protein Solvent Gum Gel Aerosol solvent General purpose rust remover paint remover urine stain remover enzymes red stain removers and several more on market
Like Dan said it is always a smart idea to have several spotting solutions with on a job, because you never know what you're going to run into. We do have a pretty thorough guide to carpet stain removal that should cover most stains.