you can use of intkey (amphipod database ) for finding family and some genera. this key are illustrated and user friendly. Also I recommend the LeCroy key for Florida amphipod. If you find the genus of material complete identification  would be achieved by special articles.

thanks Farzaneh for the help 

Bousfield, E. L. (1973). Shallow-water gammaridean amphipoda of New England (p. 312). Ithaca, New York: Comstock Pub. Associates. 

Do a google scholar search on Bousfield and Amphipod. He published many useful papers on the subject.

Those are some good keys about Amphipoda and Isopoda.

Ortiz, M., F. Álvarez e I. Winfield. 2002. Caprellid amphipods: illustrated key for the genera and species from the Gulf of Mexico and the Caribbean Sea. Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México. México D. F. 83 p

Ortiz, M., Martin, A., Winfield, I., Diaz, Y. & Atienza, D. (2004). Anfípodos (Crustacea, Gammaridea) Clave gráfica para la identificación de las familias, géneros y especies de los anfípodos (Crustacea: Gammaridea) marinos y estuarinos del Atlántico Occidental Tropical. Universidad Nacional Autónoma de México, Facultad Estudios Superiores Iztacala, México: 162 pp.

Ortiz,M. and A. Jimeno. 2001. Pictorial guide for the identification of the families and genera of Gammaridea Amphipods of the Iberian Peninsula. Graellsia; Vol 57, No 2: 3-93

Kensley, B. and M. Schotte. 1989.Guide to the marine isopod crustaceans of the Caribbean.-Smithsonian Institution Press, Washington, D.C., and London. Pp.1-308.

I also agree with the papers of Sarah Lecroy about the Amphipoda of Florida. I am also agree with Dr. Shields Bousfiled published a lot of useful papers about this topic and also can look for papers of Barnard, he also published a lot of papers about Amphipoda

Do you work on samples from the whole northern Atlantic or do you have a more precise area ? 

Another useful isopod book for the western North Atlantic is: The Marine Isopod Crustaceans (Pictured-Key Nature Series) by George A. Schultz (1969), which includes keys and distributions of marine isopods from North America. 

Jérôme Jourde

 my samples is from the atlantic coast of Morocoo ( eastern north atlantic)

You should also get "The Amphipoda of the Mediterranean" by Sandro Ruffo (Editor; 4 volumes), many species are also present in eastern Atlantic. For amphipods families and genus : Barnard, J.L., Karaman, G.S., 1991. The families and genera of marine gammaridean Amphipoda (except marine gammaroids). 2 Parts. But for these two references I only know paper versions, I don't think there are available numerical copies. The "Faune de France n°9" by Chevreux and Fage is much older but freely available, British Amphipoda by Lincoln can also be accessed on the web.

About Isopoda, as far as I know, there is no complete key for the North-east Atlantic. You have to find keys of suborders, superfamilies or lower. You can try http://isopods.nhm.org/databases/references/index.html , this a very valuable library. Biodiversity Heritage Library website can also be very useful.

If you give me a mail adress I can send you a list of references.

Good luck