I currently have a full breaker panel in my home with those small 15 amp breakers. So I really can't do much more with it. What I really would like to do before I upgrade my panel to a larger one is should I upgrade to a 200 amp service or should I stick with my 100 amp service. First of all, what's the difference between the two and what's the benefits to upgrading to 200 amp.

The difference is cost, breaker space and load capacity.

You will likely never again see a 100A service in a new home, except maybe a bare bones tract home.
To replace a 100A with a 100A is almost always not in the best interest of the homeowner.

You'll still be stuck with the 15 A breakers. The wire size dictates the maximum breaker size.

In some panels you can get twin breakers which allow two circuits to share a space. In this case, you must not exceed the number of poles for the panel.

Technically speaking it would be wise of you to have an evaluation of your service and panel done to make sure you are not exceeding the requirement of the 100 Amp Panel.

A 200 Amp Panel has longer bus lines and therefore, more space for breakers.

However, if 100 amp is all you need, then you should consider putting is a sub panel to gain additional breaker space.

If it were me facing this problem, I would first make sure my service in meets my needs. If not I would bump up to the 200 Amp service with a 200 amp panel.

If the service is close to the upper limit, I would still consider moving to the 200 Amp.

If I was mid range or below, I would stay where I am and add a sub panel.

But the real problem here is that you haven't given us any real description of your service as it exists right now.

I have a GE breaker panel. All the correct amperage for the appropriate connection i.e.. Stove 240 volts. etc. What I would really like to do is add more outlets to a room in basement that has yet to be wired. But I don't want to branch off any existing circuits since I feel these are maxed out. Your are correct in saying that I could attach a pony to my panel but I feel for the headache that it'll cause I think I would be better off installing a new panel. I have to check with my local utility to see if I'm able to upgrade to 200 amp service with my current connection from the road.

I have to check with my local utility to see if I'm able to upgrade to 200 amp service with my current connection from the road.If it is an overhead drop that is nothing you have to be concerned with. The power company owns that and will replace it at their discretion.
If it is underground you may very well own it and be responsible for it.

Overhead drop. Thank you

Get the 200A, its 2010.;) Keep that panel underloaded. I am doing more and more 400A on bigger homes these days. Additional benefits would be it adds to the homes value, most property buyers want a decent sized service. If you already think its maxed out and don't want to add load to any circuit I would definitely do it. Do you feel heat on any breakers? Have you taken some amp readings with a clamp on or anything?