What type of investment should be made?

If there is about 600 dollars to work with a month (though the amount may increase) and about 30 years to go with. There should not be a need to ever take it out, but remember, the money comes in every month.

Is there a way to add moneys to CDs? Should the money pile up in a savings account then put in a CD at the end of the year? What results in the most money at the end of the 30 years?

To answer your last question "What results in the most money at the end of the 30 years?" In the past (disclosure: past results do not guarantee future results) the answer has been investing in common stocks (or mutual funds that invest in them).
T. Rowe Price will allow you to invest in as little as $50 per month until you reach their usual minimum of $2500. They have (in my opinion) many very good funds.

Open a high interest savings account.

ING Direct is paying 4.50%, no minimums and no fees

I think the smartest way of investing is real estate. You can get great mortgages now for very little or no money down. Plus you can rent the place out and whatever is left over after the mortgage is profit. Also, in 30 years the place will be worth so much more that you can sell and make a huge profit.

with a flucating 600 a month makes me a little skissh to recommend anything seriously investment wise you cannot add money to CD's and with online banks such as ING, HSBC etc...their online savings banks offers comparable rates to CD's plus you do NOT have to tie it up for x months.

Now if you have say 1-2k to make an initial investmwent then add on to it I would say take $100 a month and put it in the online account the rest with whatever fund, etf, stock you feel most comfortable with.

You didn't give a lot of information but this is what I recommend to you.

Avoid CDs so you're not locked in. Check out www.bankrate.com for the best money market rates.

This assumes you are already saving in a IRA or 401K. If not, save enough in a money market for a rainy day fund(about 3 months on income) and put the rest in to retirement.