Size of Cells

0.1 nm (nanometer) diameter of a hydrogen atom
0.8 nm Amino Acid
  2 nm Diameter of a DNA Alpha helix
  4 nm Globular Protein
  6 nm microfilaments
 10 nm thickness cell membranes
 11 nm Ribosome
 25 nm Microtubule
 30 nm Small virus (Picornaviruses)
 50 nm Nuclear pore
100 nm HIV
120 nm Large virus (Orthomyxoviruses, includes influenza virus)
150-250 nm Very large virus (Rhabdoviruses, Paramyxoviruses)
150-250 nm small bacteria such as Mycoplasma
200 nm Centriole
200 nm (200 to 500 nm) Lysosomes
200 nm (200 to 500 nm) Peroxisomes
800 nm giant virus Mimivirus
  1 µm (micrometer)
       (1 - 10 µm) the general sizes for Prokaryotes
  1 µm Diameter of human nerve cell process
  2 µm E.coli - a bacterium
  3 µm Mitochondrion
  5 µm length of chloroplast
  6 µm (3 - 10 micrometers) the Nucleus
  9 µm Human red blood cell
 10 µm
       (10 - 30 µm) Most Eukaryotic animal cells
       (10 - 100 µm) Most Eukaryotic plant cells
 90 µm small Amoeba
100 µm Human Egg
up to 160 µm Megakaryocyte
up to 500 µm  giant bacterium Thiomargarita
up to 800 µm  large Amoeba
  1 mm (1 millimeter, 1/10th cm)
  1 mm Diameter of the squid giant nerve cell
up to 40mm Diameter of giant amoeba Gromia Sphaerica
  120 mm Diameter of an ostrich egg (a dinosaur egg was much larger)
  3 meters Length of a nerve cell of giraffe's neck

(via wikibooks)