So after listening (or is it reading?) the suggestions offered by the helpful members here, I have settled to use the IRF3205 mosfet. Seems to work well, as sayzer mentioned, you must use a resistor in the gate to pull it down, otherwise it is a bit eratic on the scope. In driving the LED strips, i have changed the strips to 5V type instead of the 12V.
I tested it with a small strip, seems ok.

The TOTAL powersupply requirement I need is whopping 18Amps @ 5VDC.
I am ready to connect ALL the strips and before I blow anything up (again), I have a question.

I have 2 switchmode powersupplies, <a href="http://jaycar.com.au/productView.asp?ID=MP3123&CATID=27&keywords=&SPECI AL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pag eNumber=&priceMin=&priceMax=&SUBCATID=647">Powersu pply</a>

On the casing they are rated 10Amps for the 5V. Can also do 24V @4.5amps (but not needed)
Is it possible (and safe) to connect the outputs in parallel to achieve a 20Amp capacity?
My other idea was to use a computer PSU where normally the +5V DC rail can deliver up to 30Amps.
Not quite sure how else I can achieve a high output PSU.