http://www.knowledgebydesign.com/tlmc/tlmc.html
A linked movie at this site illustrates a rotating model of DNA. A model of an enzyme can also be viewed from a link on this site.

http://esg-www.mit.edu:8001/esgbio/cb/org/animal.gif
A beautifully colored illustration of an animal cell but with no links.

http://esg-www.mit.edu:8001/esgbio/cb/org/organelles.html
This illustrates a plant cell but the site has links to additional pages on the nucleus, ribosomes, and mitochondria. At these sites you will find drawings and/or electron micrographs.

http://lenti.med.umn.edu/~mwd/cell_www/chapter2/mitochondria.html
A picture and brief description of a mitochondrion.

http://lenti.med.umn.edu/~mwd/cell_www/cell_intro.html
A good picture of the cell membrane and its constituents.

http://lenti.med.umn.edu/~mwd/cell_www/chapter2/membrane.html#SEMIPERM
Additional details about the chemicals that make up the cell membrane and a discussion of osmosis and diffusion.

http://lenti.med.umn.edu/~mwd/cell_www/chapter2/protein.html#MEMBRANE
Active transport proteins are discussed, and linked pictures illustrate their action.