Try Buy.com at the following link for an example (you will want to make sure the exact type of memory you need; if you write back with your exact computer specifications, we can check for you, although most memory sellers have a way of entering your iMac into their system and they will tell you what you need). BTW: Kingston has always done well for me, but everyone has their preferences when buying memory.
I have the following iMac 20" and was wondering if this 2gig and 1 gig memory kit will work fine http://www.buy.com/prod/corsair-3gb-ddr2-sdram-memory-pc2-5300-200-pin-sodimm/q/ loc/101/204347447.html?dcaid=17905
Intel Model Name: iMac
Model Identifier: iMac5,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.16 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache (per processor): 4 MB
Memory: 1 GB
Bus Speed: 667 MHz
Boot ROM Version: IM51.0090.B09
SMC Version: 1.9f4
Serial Number: SystemSerialNumb
Here are a couple of 4GB kits for under a $100
[newegg-4GB CORSAIR|http://www.newegg.com/Product/Product.aspx?SID=481053-9-0-RAM-0&Item=N8 2E16820145193&ATT=20-145-193&CMP=OTC-dealram&nmmc=OTC-dealram&cm_mmc=OTC-dealram-_-Memory(Notebook+Memory)-_-Corsair+Memory+Inc.--20145193]
[dealram 2x2GB|http://dealnews.com/memory/prices/systems/Apple-i-Mac-Intel-PC2-5300-DDR2 -SO-DIMMS/41494/2GBx2.html]
Unless I'm missing something, the link you gave was to a single 3gb chip, which will NOT work with your iMac, from what I have researched.
Your iMac can take up to 2gb in each slot, but can only handle up to 3gb total. It came with each slot having 512mb in it, so these will have to be removed and sold or trashed.
You could put a 2gb chip on one side and leave a 512mb in the other for a total of 2.5gb. Many people will tell you to use only matched pairs, which has a slight benefit, but the greater benefit is from having more RAM overall!
Or, you could put 1gb on one side and 2gb on the other side for a total of 3gb. You decide.
Here is a link to a page with your iMac's specifications: http://www.everymac.com/systems/apple/imac/stats/imac-core-2-duo-2.16-20-inch-sp ecs.html
Here is another one that explains why 3gb is the maximum RAM for your system: http://www.memory-up.com/Memory/AppleiMac14834.html
No, the link is for a 3gig kit, with 2 gig and 1 gig chips. I want to make sure that the iMac can handle that. According to the manufacturer's website, it can. But i have read in the past that it is best to use the same size pairs in the slots which makes no sense since the imac can handle up to 3 gig and there are no 1.5 gig chips
It looks like Buy.com is in error listing that 3GB upgrade, here is the same upgrade # from another supplier that shows the upgrade as 1x1GB and 1x2GB modules.
Yes, I googled: Corsair VSA3GSDSKIT667D2 from your Buy.com link to find other suppliers selling that upgrade kit. At the time I was more concerned that someone was trying to mislead and(or) sell us a 3GB module than the price. Most folks won't have any use for a 3GB kit in there new iMac, it already has a 1GB module. They need a 2GB module to bring there system up to 3GB or 2x2GB to bring there system up to 4GB.
By the way look down at my post to the OP, the 4GB kit from newegg is a better deal!
*I have had great experiences with OWC* (aka MacSales.com). My last 4 Macs were all upgraded with memory from OWC.
*I would avoid Buy.com*
They have the worst reputation for service.
Don't take my word for it, just surf to http://www.resellerratings.com/store/Buy and what their customers/victims have to say.