I drive a 2007 Tacoma. This is my fourth pickup (second Tacoma) and I am sold on Toyota. The only reason I traded my old '04 for the '07 was to go from extended cab to double cab. I have no personal experience with Nissan products, but I would definitely advise you to go with a Toyota based on my experience with my two. I don't get quite as good of gas mileage as the guys who have posted here so far but I also drive a 4x4 truck in San Diego traffic. I average 17 mpg compared to the 20 mpg I got when I lived in Milton.
The truck itself is rock solid (as was the '04). I bought the double cab model for the extra space and have been thoroughly pleased. I grew up driving full size, American-made trucks and was a little skeptical at downsizing to a midsize/compact. For Toyota, model years '05 and newer are MUCH LARGER on the inside. I found myself feeling cramped in my '04 if I needed to fill the cab with gear or drive any people around. The newer body style affords much more interior room and I absolutely love it.
To the original poster, I know you're looking at getting a 4-cyl model. If you don't have your mind made up about that I'd urge you to at least consider a 6-cylinder engine. At least test drive the two before you make a decision. Like someone else said, if you're going for MPG then get a car. If you need the utility of a truck I think you'll find yourself much happier with a V-6.
Feel free to ask/PM me anything about the '04, the '07, Toyota in general, or anything else.
Gatordev - I wouldn't recommend towing a 4000# load with a Tacoma unless you get a 2005 or newer. The engine will do fine with that much weight. You'll need to see your dealer about the rear suspension though. A lot of people who tow/carry heavy loads have found the rear leaf springs to be inadequate. Toyota will replace them under warranty. I have a lot more information on this subject if you're that interested.