First gen is 1995 to 2004, second gen is 2005 to current. I guess 2013 or 2014 will be the last year for the current Tacoma, though. Speculation (probably wishful) is the Tacoma will converge again with the Hilux, more or less. If Toyota extends the current Tacoma platform an extra year or two that is a good sign. Worldwide Toyota runs a Hilux design for roughly 9 years, it changed in 1997 and 2006. The Tacoma was running a year or two ahead, so if they hold over the current platform beyond 9ish years it could mean they want the two truck product cycles to overlap again.
Toyota does cosmetic changes on the trucks periodically, in the case of the 3rd gen Pickup the body style ran 1989 to 1991 and then 1992 to 1995. When they do a model revision they do change things, like in 1992 the grill changed. They also added electronic speedometer and changed a few interior pieces. But mostly the mechanicals don't change and are largely interchangeable.
In the Tacoma they were less distinct, they seemed to do more rolling changes. Some mechanicals seemed to change in 1997, cosmetics changed in 1998 to flush headlights but 1999 had changes to the air box. The last cosmetic generation was 2001 to 2004, with the bumped hood and stuff.
'91 Toyota Pickup
'09 Kawasaki KLR650
'12 Gunnar Rockhound 29
"To live is to suffer, to survive is to find some meaning in the suffering." -- Friedrich Nietzsche