We hear a lot about incarnations of Lord Vishnu, Lord Shiva and other Gods, but were there any incarnations of Lord Bramha too?
Yes, Brahma has taken incarnations. Here are two of them:
Chandra: As I discuss in this answer, there was once a Brahmana named Kaushika who received a curse from the sage Mandavya that he would die at sunrise. As a result Kaushika's wife, who had magical powers, stopped the sun from rising. So the world was engulfed in darkness, and the gods turned Anusaya, wife of the sage Atri who was a mind-born son of Brahma, for help. Anusaya convinced Kaushika's wife to allow the sun to rise in exchange for Anusaya using her magical powers to save Kaushika's life. The gods were pleased with Anusaya and offered her a boon. Anusaya asked that Brahma, Vishnu, and Shiva should all be born as her sons. They agreed, and soon enough Brahma incarnated as Chandra the Moon god (AKA Soma), Vishnu, incarnated as Dattatreya, and Shiva incarnated as the angry sage Durvasa. Here is how their births are described in chapter 16 of the Markandeya Purana:
The moon, the stay of the life of all creatures, was born as the mind begotten son of the patriarch Atri. Well-pleased the high-souled Vishnu was born from his own body as the best of the twice-born, Dattatreya permeated by the quality of goodness. Incarnating himself Vishnu was born as the second son of Atri known under the name of Dattatreya who sucked the breast of Anusuya.... Then was born Durvasa, a portion of Rudra impregnated with the quality of darkness. Thus Brahma, Vishnu, and Siva were born as her three sons. By virtue of the boon conferred upon her by the celestials Brahma was born at the moon, Vishnu as Dattatreya and Sankara as Durvasa.
Vikhanasa: Mainstream Vaishnavism is based on a set of scriptures known as Pancharatra. The Pancharatra texts consist detailed procedures to worship the sage Narayana, an ancient incarnation of Vishnu and twin brother of the sage Nara. (Arjuna and Krishna were reincarnations of Nara and Narayana respectively.) Since the Pancharatra texts originated from Vishnu himself, they are followed by pretty much all mainstream Vaishnava Sampradayas, whether Sri Vaishnavas, Madhvas, Gaudiya Vaishnavas, etc. (For more information on the Panharatra texts, see my questions here.)
But as I discuss in this question, there is another group of Vishnu-worshippers who worship Vishnu according to a different set of texts, the Vaikhanasas. They're a tiny minority among worshippers of Vishnu, but for instance they're in charge of the famous Tirumala Venkateshwara Temple. In any case, the Vaikhanasa tradition was founded by Brahma's incarnation Vikhanasa, as described in this excerpt from S. Rangachar's book "Philosophy of Pancaratras":
Brahma incarnated himself as Vikhanas in the Naimisharanya and then Vishnu Himself taught Brahma the mysteries of worship in the form of thirty two questions. Since God, the Bhagavan himself taught this Agama to Brahma first, Vishnu Himself is the originator of the Agama also as in the case of Pancharatra Agama. As it was Vikhanasa who gave this Agama to the world directly through his four disciples or Maharishis, namely Atri, Marichi, Kashyapa and Bhrigu, he is as said to be the Pravartaka of this Agama and hence the agama is called after him.
And then those four sages are said to have composed texts of their own in the Vaikhanasa tradition.
On a side note, putting these two stories together, we get the interesting conclusion that Atri was the father of one incarnation of Brahma and the student of another, all the while being the son of Brahma himself!