Popcorn cells are seen in:
Hodgkin lymphoma is currently classified in the following manner:

Nodular lymphocyte-predominant Hodgkin lymphoma.
Classical Hodgkin lymphoma (comprising five histopathologic subtypes):


Lymphocyte rich
Nodular sclerosis
Mixed cellularity
Lymphocyte depletion
Unclassifiable

These names describe the most prominent histopathologic feature of each type, and specific epidemiologic and prognostic characteristics are associated with each type. Nodular lymphocyte-predominant Hodgkin lymphoma constitutes 4% to 5% of all cases of Hodgkin lymphoma in the United States. In the past, this form was probably combined with the lymphocyte-rich subtype, but the presence of the characteristic popcorn cells is a significant clue to the diagnosis. 
 
Ref: Oral pathology Neville, 4th ed page no 554
Hodgkin’s lymphoma
Non-Hodgkin's lymphoma
Burkitt’s lymphoma
Multiple myeloma