Of all the images I've uploaded to Wikipedia, these are some of my most favourite:

3D chemical structures

Inorganic compounds

• 
  Carbon dioxide
• 
  Ozone
• 
  Water
• 
  Phosphine
• 
  Phosphorus pentoxide
• 
  Phosphorus tribromide
• 
  Phosphorus pentachloride
• 
  Diborane
• 
  Decaborane
• 
  Sulfur
• 
  Aluminium chloride
• 
  Hydrogen sulfide
• 
  Sulfur dioxide
• 
  Sulfuric acid
• 
  Thionyl chloride
• 
  Sulfur dichloride
• 
  Sulfur hexafluoride
• 
  Tetrasulfur tetranitride
• 
  Ammonia
• 
  Hydrazine
• 
  Dinitrogen tetroxide
• 
  Uranium hexafluoride
• 
  Uranium dioxide
• 
  Sodium chloride
• 
  Caesium chloride

Organometallic compounds

• 
  Zeise's salt
• 
  Zirconocene dichloride
• 
  n-Butyllithium
• 
  Uranocene

Organic compounds

• 
  Firefly luciferin
• 
  18-crown-6
• 
  Triflic acid
• 
  Ethanol
• 
  Methyl isocyanate
• 
  Benzene
• 
  Phenol
• 
  Phenol
• 
  Ethylene
• 
  Diethyl ether
• 
  Acetic anhydride
• 
  N-bromosuccinimide
• 
  Formic acid
• 
  Ethanethiol
• 
  Arsole
• 
  Lawesson's reagent
• 
  Dimethylsulfoxide
• 
  Acetone

Biological molecules

• 
  Glycine
• 
  Trimyristin
• 
  Linolenic acid
• 
  Thiamine
• 
  Acetyl CoA
• 
  NADH
• 
  DNA
• 
  Glutathione
• 
  Oleic acid
• 
  ATP
• 
  Glucose-6-phosphate

Drugs

• 
  Chloramphenicol
• 
  Furosemide
• 
  Paroxetine
• 
  Methoxyflurane
• 
  Cimetidine
• 
  Heparin

Pesticides

• 
  Malathion
• 
  Chlorpyrifos

Photographs

• 
  Trifle
• 
  All Saints, Odell
• 
  Odell Castle
• 
  The Bell, Odell
• 
  Ambulance
• 
  Bedford Hospital
• 
  Chip-pan fire
• 
  Mercuric oxide
• 
  Phenolphthalein