If you are looking to spend $100 or less, Water Cooling is out of the question.
A good Water Cooling setup is quite expensive.
The cheaper ones are erally not worth having IMHO, as many of the higher end air coolers can do nearly as good cheaper.
As stated, you do NOT
need a water cooling set up, unless you plan on very extreme Overclocks.
I would say replacing the stock cooler is a good idea.
My recomendation would be:
An Air Cooler something Like Xigmateks 1283s are excellent coolers, and far superior to the stock heatsinks. Newegg.com - XIGMATEK BALDER SD1283 120mm Long Life CPU Cooler I7 i5 775 AMD compatible, w/ bracket ACK-I5361
Also, some good thermal paste to go with it. I really like MX-2
, and have had very good luck with it.
There are plenty of other good air coolers and thermal paste out there, and you will get many good suggestions.
I personally really like Xigmatek, because the do an excellent job, at a great price point.