It depends on what the itch is caused by. If it is systemic, then antihistamines. If it is topical then the above recommendations but here is a link to learn about more remedies. http://www.herballegacy.com/search.php?zoom_query=itch
If it is from poison ivy or oak then that is something different and the list goes on.
Being in the woods as much as I am, I'm always getting stung or bit by something. I've used a product called StingEze, by Wisconsin Pharmacal Company for years. A $5 bottle lasts me for a year or two. It works great for mosquitoes, chiggers, ticks, wasps, and even poison ivy. The active ingredient is Benzocaine. You can get it online or at your local drugstore, I get mine at walgreens. For poison ivy, the BEST stuff ever is called "Tecnu Extreme medicated Poison Ivy scrub"- it literally scrubs away the oils, completely eliminating the itch. This stuff is better than anything I've ever tried. Try it, you'll be amazed. A definite for the first aid kit.