OK so I'm trying to find out what the most common, and reliable art programs are out there for producing digital artwork. I currently use Photoshop Elements, however I'm on the fence about getting something new like Paint Tool SAI or something more advanced that I can start learning how to use.

I'm a huge fan of Sai! It's lightweight (if you've got a struggling laptop like me) and intuitive - that is, the tools are easy to use and the user interface is clear - and a lot more user/beginner friendly than photoshop. It's also a hell of a lot cheaper than PS. You could also look up some sai tutorials on dA and see if it's for you. If you're leaning towards PS anyways, I know adobe released CS2 for free on their website. Perhaps you can check it out before investing in later versions? 

Well I was leaning towards SAI since like 90% of artists use it at least once in their career/hobby. I need to start getting into the main stream with everyone else since I think the version of PS Elements I have now is just not cutting it for what I need.

Hi! This thread is a little old but maybe someone might find this info useful.

Another good art program is tle="" href="https://krita.org/en/">Krita, it's free and pretty much made for digital art. It might have a bit of a learning curve but there are so many brushes and a lot of neat things that I enjoy using it for sketches and some painting stuff.

If you want to pay some moola though, tle="" href="http://www.clipstudio.net/en">Clip Studio Paint/Manga Studio is another good art program. It can be pretty expensive, like the EX price is pretty outrageous, but the EX version is NOT a necessity, it just adds 3D models and some other stuff. It has sales sometimes that make the price a little more reasonable, but the PRO version is just fine for most people.

I personally use CSP the most, and it's probably because the interface is very clean and not very confusing. Also, with some custom brushes downloaded I can do pretty much the same stuff I did in any other program.

Also if you like SAI I believe there is a demo for SAI 2 available tle="" href="https://www.systemax.jp/en/sai/devdept.html">here for anyone interested in the new version!

I've been using a pirated version of like, 2008 paint tool sai for years and its never done me wrong. I'm sure the newer versions of sai are even better but it's been getting the job done for me since 2012.

I also have photoshop CC 2015 and photoshop CS2, but I very rarely use them, like almost never. Pretty much anything can be done in sai with photoshop as a backup if sai is lacking whatever.