Hayden Part No. 678 or 679 - either one. Both are of the stacked plate design, too. Pep Boys sells them for about $60-$70, but I've heard of people getting them on ebay for about $30-$40. Summit Racing sells a bunch of different trans coolers, too.

Also, it helps to buy extra trans cooler hose - but make sure it is labeled as transmission cooler hose and not something else, like fuel line. Fuel line is not designed to handle hot, 150-250 degree fluid. And the bigger the hose diameter, the better.

It's true that a stacked plate design dissipates heat more efficiently than a tube and fin design. However, a tube and fin design is much less restrictive with flow than a stacked plate design. Flow restriction is also a tranny killer, but most stacked plate designs do not restrict the flow so much to risk starving the tranny of precious fluid and pressure to the point of damage, unless you run two or three in series. The best setup is a big tube and fin cooler with an electric fan and shroud in which the core is at least 1.5" thick (the Hayden 678 and 679 cores are only 3/4" thick for comparison). But unfortunately, it's not only expensive ($150-$400), but it's also very difficult to fit in front of the Tacoma's a/c condensor without major cutting and modification.

An old school trick is to get a good, clean a/c condensor from a salvage yard and run it as a tranny cooler, but you have to make sure it's super clean inside and has not suffered "black death" damage, otherwise you'll be contaminating the transmission with blackish gunk and possibly killing it. Also, most a/c condensors are huge, which obviously makes them excellent heat dissipation units, but also makes them hard to fit behind the front grille of a Tacoma.

Hope this helps.