The Zetex range work well in low voltage circuits. The ZTX851
has a 5A (continuous, 20A peak) rating and ~0.1V saturation
at 2A

http://www.zetex.com/3.0/pdf/ZTX851.pdf

However, as it's in an E-line package not a lot of W. Possibly
more suitable for pulses (PWM, eg IR LEDs) than static loads,
but if W is in the ballpark it may do

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