Sigma Aldrich - huge selection, good price, normally fast delivery.
Merck Chemical- huge selection, good price. Typically highest purity of any company.
Johson Matthey- big selection, mostly metal based materials.
Fischer Scientific- big selection, good price
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Companies to buy consumables/small lab equipment
VWR- huge selection, approved for use in laboratory setting. However expensive compared to a regular hardware store.
Fischer-Scientific- huge selection, approved for use in laboratory.
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Companies to buy large equipment
AJA- Vacuum equipment. We have one of their sputtering systems and our happy with it
Lesker- Vacuum equipment. I have seen their systems in work and they seem good.
Shimadzu- They sell GC's, UV-vis, etc.
Agilent- They sell GC's, UV-vis, etc.
Optics companies
Thor Labs - Relatively fast and cheap. Wide variety.
Oriel/Newport - Probably the highest quality and resepctable prices.
Ocean Optics - Cheap, portable solutions
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Other useful Companies
Lab-X- A respectable place to buy used laboratory equipment