This article is from the U.S. Civil War FAQ, by Justin M. Sanders email@example.com with numerous contributions by others.
[31 Aug 1861 will be the cut-off date for this answer.]
Generals in the CS Army (all were appointed on 31 Aug 1861, to date
from the date given below):
Samuel Cooper 16 May 1861 (Adjt & Insp. Gen)
Albert Sidney Johnston 30 May 1861
Robert Edward Lee 14 Jun 1861
Joseph Eggleston Johnston 4 Jul 1861
Pierre Gustave Toutant Beauregard 21 Jul 1861
Prior to 16 May 1861, the highest rank in the CS Regular Army was
Brigadier General (5 were authorized):
Samuel Cooper 16 Mar 1861 (Adjt & Insp. Gen)
Robert Edward Lee 14 May 1861
Joseph Eggleston Johnston 14 May 1861
In addition to the CS Regular Army, there was the Provisional Army (PACS).
Which had the ranks of Brigadier and Major General.
Major Generals (PACS):
David Emanuel Twiggs 22 May 1861
Leonidas Polk 25 Jun 1861
The first Brigadier General (PACS) was
Pierre Gustave Toutant Beauregard 1 Mar 1861
at least 35 others appointed between Mar and Aug 1861
The rank of Lieutenant General was authorized for the PACS on 18 Sep 1862.