The Classical Era in musicology roughly dates from 1730 to 1820 with some margins because of the view of musicologists. I for instance read that some start the classical era with the death of Johann Sebastian Bach (1750).
An obvious aspect in the classical musical style is a stricter separation between melody and accompaniment. The consequence was more attention for expression and dynamics in music. The important function of counterpoint that marked Baroque music had less focus in the classical period. One of the major forms in the Classical Era became the Sonata, often in three movements with a tightly organized organisation of the music within.
In the Classical Era, the guitar flourished. From the number of guitar instruction methods published in this time it is obvious that there was a lively interest for the instrument. The popularity of guitar ensembles with two or more guitars and melody instruments became popular.
The main representatives of the Classical Era are Fernando Sor (1778-1839), Fernando Carulli (1770 – 1841), Mauro Giuliani (1781 – 1829), Matteo Carcassi (1792 – 1853), Niccolo Paganini (1782-1840) and Dioniso Aguado (1784 – 1849).
The DOS Amigos Homepage features a collection of about 20 duo pieces from this period.