OK, this is a little extreme, but you get the idea for how easy side jobs can be. Source: revolution cycle, via Wikimedia Commons. 

Listen, few have ever gotten rich off of side jobs alone. But if your main gig isn't providing the type of cash flow you hope for, side jobs can make a huge difference in helping you meet your financial goals.

In that spirit, I looked for side jobs that offered two key benefits: flexibility and ease. No one wants to mentally tax themselves during their down time, and if a job requires too much effort or resources, it probably won't make a good side job.

Here are the six top side jobs I found, with potential pay included.

1. Donate yourself
Ok, I'll admit, donating bodily fluids doesn't really qualify as a "side job." But it does represent a form of compensation that is easy and offers a tremendous amount of flexibility. The most common form of donations are blood and/or plasma. With blood, you can only donate once every eight weeks, while plasma can be donated much more often.

Believe it or not, there's a large market out there for breast milk as well. Sometimes, moms who are overproducing can offer their milk for as much as $2.50 per ounce, according to this 2011 Wired article.

Then there are more personal decisions. Donating sperm or eggs can be lucrative, but many may shy away from the thought, because not knowing if there's a little one running around with your DNA seems overwhelming.

In every case except for breast milk, some form of screening is usually involved.

  • Donating plasma/blood: $50 per session
  • Donating breast milk: Up to $2.50 per ounce
  • Donating sperm: Up to $1,000 per donation 
  • Donating eggs: Up to $8,000 per donation 

2. Substitute teaching
For some, the idea of substitute teaching sounds awful. But consider the stay-at-home mom or dad that likes being with kids, and is good in front of them. For these folks, substitute teaching offers a great way to connect with the community, get out of the house, and get paid. It's also not a bad choice for those who have just gotten their teaching degree, but not yet landed a job.

The amount you can be paid for substitute teaching varies widely, with certified teachers, or long-term substitutes, often earning more. No matter your background, though, there's a shortage of substitute teachers. If you impress the administration, you could have a job as often as you like.

  • State with lowest-paid substitute teacher rate: South Carolina, $35 per day.
  • State with highest-paid substitute teacher rate: Minnesota, $141 per day.

3. Bartending
Here's another job that's very hit or miss when it comes to pay. If you work Friday and Saturday evenings at a bar that's popular, you could easily end up making over $1,000 per weekend. But competition for those slots is high, and it often requires a lot of energy, too.

Do not attempt without proper training! Source: Tom Purves, via Wikimedia Commons. 

If you're looking to see if bartending is for you, it's best to start small. Ask your local brew house what you might have to do to work a mid-day or early evening shift during the week, and go from there. Usually, this will require a little work on your part, as you'll need to get your bartending license. While the job is exciting and could pay a lot, it certainly isn't for everyone.

4. Babysitting
Babysitting isn't the easiest job in the world, but if you have established a connection with the kids you are looking after, it isn't the toughest, either. And it can be really rewarding.

While looking after someone else's kids full time might not be what you're looking for, lots of parents are looking for sitters on the weekends and at night so they can sneak out for a couple of hours.

Care.com is a great place to start: The site is designed to match parents with potential sitters of varying experience and availability levels. Pay varies, but it's usually within a pretty tight range.

  • Nationwide average: $13.44 per hour
  • Best babysitting rates: San Francisco, Calif., $16.65 per hour
  • Worst babysitting rates: Grand Rapids, Mich., $11.31 per hour

5. Tutoring
I know I said side job work shouldn't be mentally taxing, but I'm making an exception for tutoring. That's because you are likely an expert in a subject area without even knowing it. The types of skills you've come to rely on every day in your job might seem ordinary to you, but to a struggling middle schooler, you're the equivalent of a rocket scientist.

Again, this job isn't for everyone -- an ability to connect with a child and break down complex ideas into digestible parts is crucial. But if you can do it, Angie's List reports that tutoring sessions can be truly lucrative.

  • Private, at-home tutoring: $15-$85 per hour, depending on experience level

6. Dog walking
Here's one of the few side jobs you can actually scale -- to a degree. Urban areas are teeming with dog owners who spend most of their waking hours at work. Someone needs to take all of those hounds out for a walk, and that's where this burgeoning industry comes in.

Establishing a reputation within your neighborhood can make a big difference, but even a few daily half-hour gigs can help bring in lots of cash -- according to dogwalker.com. If you walk three dogs per day -- all at the same time and within the same neighborhood -- you could easily bring in $90 extra bucks... each day!

  • Average rate: $10-$30 per dog per half-hour walk.

Not all of these jobs may sound appealing to you. But usually, there's at least one side job out there that requires a minimal amount of effort on your part and can help augment your income. If you don't see anything that appeals here, and you're "of age," consider checking out the special report below to increase your Social Security payouts.