I would avoid proprofs and certblaster. They are unreliable and using them could force you to learn wrong information. Avoid like the plague. Same with preplogic. I'm not going to beat around the bush and will just tell u straight up they are utter crap(despite what others say)

i have tried lots of different test questions for the net+ and security+.Best i found were Mike meyers (the 300odd question version which can be bought online), killtest. I also had a 900 question net+ test engine which helped alot. There's also some in Glen E Clarke's book as end of chapter tests. Then there's SYbex net+ book and cd. They are OK but there's mistakes in them which unfortunately seems to be the norm with sybex material.