Desktop publisher - creating brochures, fliers, and custom business cards ect. Save yourself the time and find a good wholesale printer. Most of the work you will be doing is the creative.

Cost: Computer 1000 dollars
Desktop software 50-400 dollars

Web Designer - create simple 5 page websites for small businesses who want to get their name out. Start simple and small = fast return on investment.
Start up cost:
$500 - 2000 for a computer.
$50 - 500 Web Design Software
I personally recommend dreamweaver if you want to get serious about web design or the macromedia suite.

Web consultant - help clients increase their internet traffic.
Start up:
0-200 dollars depending on what search optimization you're using to help your clients.

Ebay Seller - sell items on ebay
Find products that you have around your garage. I've sold used clothing that I thougnt no one would buy. Guess again right?

Ebay instructor - teach people how to use ebay and how to sell ebay. Start up for this will normally be the rental of a room.

Ebay agent - sell items for others. This is useful if you have a good record on ebay.
Cost
Varies on listing fees 2-6 dollars an item.

Mobile DJ Service
The cost mostly comes into play when your deciding what type of equipment to buy. My simple advice is not to go cheap on the speaker, amp system. It will cost in the short run but will pay dividends in the long run.

Cost 1000 to 2000 dollars in equipment.

Lawn Care - You can specialize in tree services, landscaping. Normally in the summer you will be able to get more jobs.
Cost 200 to 1000 dollars.

Baby Sitting Services -

Dog Services - Taking care of dogs and dog walking services.

Photographer - Depending on your budget you can start as little as 200 dollars. There are many people who would pay for services besides the usual wedding.

Herb Farmer - Herb Farming does not require to much of an investment as well of time and space. A good way to make extra money. Especially if the herbs are grown organically.