There are a lot of sites selling components and to research them all is a daunting task. To make your job easier, we have compiled a small list of online stores selling resistors, with links to the relevant section, where possible.
Amazon.com: carries a vast selection of SMD and Through-Hole resistors including carbon and metal film, from 1/4W to several Watts and many quality resistor kits:
MCMelectronics.com: a large selection of carbon, metal film, flameproof and wirewound resistors and a few resistor kits.
Ebay.com: eBay is a great place for cheap or hard-to-find components. Resistors are no exception -- a quick search on resistors reveals a lot of listings.
There are also a handful of stores specializing in cheap electronic components from China, Taiwan, Hong Kong, US, etc., usually with worldwide shipping. For example, see Thai Shop Etc (shipping from Bangkok, Thailand), Eric Cheung Electronic (Hong Kong) and Electronic Parts Warehouse (United States) and many more.
Maplin.co.uk: Maplin Electronics Ltd ships only to UK, Channel Islands and the Republic of Ireland. The online store stocks a wide range of resistors: metal film, high power wirewound and a few resistor packs.
Other stores: Rapid Electronics Limited (UK), Farnell (UK), Digi-Key, Frys, Mouser...
See also:
Where to buy capacitors and LEDs online
Resistor color code calculator
Standard resistor color code examples:
E12:
.1Ω-.82Ω,
1Ω-8.2Ω,
10Ω-82Ω,
100Ω-820Ω,
1k-8.2k,
10k-82k,
100k-820k,
1M-8.2M.
E24 series - E24 series (5%) - color codes, shorthand notation and tolerance range.
E48 series - E48 series (2%) - color codes, shorthand notation and tolerance range.
Surface mount resistor code calculator
SMD resistor code examples: 3-digit, 4-digit and EIA-96.