MOSFET or bipolar to drive a solenoid valve?
I'm afraid I don't agree with Matt's conclusions.

You can find BJTs with low saturation voltages. A quick search at Digikey turned up this one. At 1 A the saturation voltage is typically 45 mV, that's equivalent to a FET with an \$R_{DS(ON)}\$ of 45 m&Omega;. Not bad at all for a BJT.
And even the 200 mV Matt used as a typical value is absolutely no problem: at 0.67 A that's 130 mW, and the "lot of wasted energy" after a year of continuous operation is 1.17 kWh. For the NSS60601MZ4 that's 0.26 kWh. Not what I call "a lot".

The problem lies elsewhere. The minimum \$h_{FE}\$ of 120 at 1 A is specified for a \$V_{CE}\$ of 2 V, i.e. the transistor is not in saturation. The 45 mV is for a base current of 100 mA and 1 A collector current. Now that's what I call a waste: the 100 mA doesn't flow through the load at all. If you control the transistor from a microcontroller you'll have the problem that a microcontroller can't source that much current. And, finally, the datasheet notes that the 100 mA is pulsed, so it may not be able to do this continuously (though I couldn't find a maximum value for base current).

That's the problem with BJTs, especially for currents higher than about 0.5 A. And here the MOSFET shines. Drive current: near zero. \$R_{DS(ON)}\$: what you want to pay for, 1 m&Omega; is possible. You'll have to look at the minimum gate voltage; for driving by a microcontroller you want a logic level gate FET.  

So, if FETs are so great, why do we still use BJTs? Cost. A BJT may be 50 % cheaper than a FET. It's that simple really.

edit
Scott mentions a Darlington to overcome the driving current problem with the BJT. I failed to mention it, and I should have. Not because it's a solution, but because it's not! A Darlington has a (much) higher saturation voltage than a common BJT; I've seen values up to 4 V maximum. But even 1.5 V would be much if you have a low voltage supply like 12 V: the reduced voltage across the solenoid means that only about 75 % of the required 8 W is available, and that may be too little to activate the solenoid. Also, the transistor will dissipate 1 W, and a Darlington is more expensive than a common BJT, so the cost advantage doesn't count either.