Prolific winger Simao and striker Almeida signed contracts on Friday that pledged their services to the Istanbul club until the end of 2012-2013 season.
Simao and Almeida will team up with Portugal international teammates Ricardo Quaresma and Manuel Fernandes at Beşiktaş, who also boasts Spanish superstar Guti.
Despite several big-name signings, Beşiktaş failed to live up to expectations so far, since it is fifth in the standings, 14 points behind league leader Trabzonspor halfway through the season.
Simao and Almeida will try to lead the team upward, but Beşiktaş is likely to cope with foreign player limitations.
With latest additions, Beşiktaş has 14 foreign players in its squad, four more than the Super League regulations allow. Teams can use six foreign players during a Super League game, and a further two of them can be on the substitutes’ bench.
On Thursday, Portuguese international Simao Sabrosa bid a tearful farewell to Atletico Madrid, the Associated Press reported.
"It's difficult for me to talk right now. I want to thank the club for having faith in me and paying so much to Benfica to sign me," said Simao, who joined Atletico in 2007 from Portuguese side Benfica for 20 million euros.
"I don't think I have defrauded anyone. When I arrived I said I would do my best to win a title and I eventually ended up with two in Europe," he added, fighting back tears. "It hurts to leave this club because it is where I have had the most friends and where I have felt at home."
The 31-year-old winger helped Atletico win the Europa League and the European Super Cup in 2010 and was popular with his teammates and fans, but his contract with the Spanish side was set to expire at the end of the season.
Atletico president Enrique Cerezo hailed Sabrosa as "an example of professionalism, commitment and dedication to his work."
Sabrosa scored the only goal of Atletico's 1-0 win over Espanyol in the King's Cup on Wednesday in his final appearance for the team.
Beşiktaş secured the services of striker Hugo Almeida from Bundesliga side Werder Bremen for two million euros.
The 26-year-old - scorer of 12 goals in his 33 international appearances - signed contract with Beşiktaş after his wage demands were refused by the Werder Bremen board.
