Hi,
How many of you remember what Taco Bell used to be? (Dedicated to the memory of Taco Bell founder Glen W. Bell, Jr., who passed away this January 17th at age 86.)
As to their buildings, between 1962 and 1985 they all resembled mission buildings with their bell-like structures (there was even an opening for a facsimile of a bell). After 1985, the chain's buildings took on a more standard approach decade-wise.
#1a - A typical 1979-85 Taco Bell had looked like this:

#1b - This is perhaps a Taco Bell from before 1979, due to the stucco:

(Note replacement signage from at least 1994 - original logo was either the "tippy blocks" which spelled out "TACO BELL" or red lighted letters reading the same)
#2 - Another pre-1985 Taco Bell but with 1985-93 signage:

#3 - A post-1985/pre-1994 Taco Bell had looked like this:

#4 - And let's not forget the old-style road sign that was in use from 1962-1985:

Photo credits from Flickr:
#1a, 1b, 3: Darrell James
#2: Andrew Turnbull
#4: T.W. Collins
~Ben