name-brand companies like kingson, crucial, corsair, and simpletech have lifetime warranties on their products, however, corsair has the best warranty if anything goes wrong (and they have an identifiable sticker on their products - don't take it off!). if you must RMA memory, make sure you package it in at least a pink poly bag (which doesn't generate static) or a nickel-plated static-shielding bag (if you want them to do something that is). they will check the memory out for damage. when you handle memory, remember friction and separating of surfaces causes static, and static destroys memory. the more GB it is, the more sensitive it is. I suggest you get the static out of your clothes before you do this. You should handle it from container to slot using a conductive wrist strap - you can probably get one at Radio Shack. If you don't have a wrist strap, and you can manage it with one hand, have one hand constantly in contact with the computer case that you are installing the memory into (it doesn't have to be grounded - you and the case and the memory just have to be at the same potential). Install the largest capacity memory module first. save your memory carriers. you never know when you might need one. Memory companies will help you identify your memory type, usually without opening your case. You should know your computer make and model number, for instance a Dell Dimension 2400.
memory heat spreaders, available at Newegg
required for higher-speed RAM. or you have meltdown.
Corsair - memory for overclockers/high-performance memory. this stuff may have heat sinks on it. seems to have a good RMA policy. They carry PC-133 too.
Crucial - expensive. worth it. has web site with ActiveX control that identifies your PC's memory type & suggests upgrades (but doesn't distiguish between CL2/2.5/3). good RMA policy from my experience. has higher-capacity memory. sells server memory. Identifiable company sticker. Uses Micron.
Kingston - also appears to have a good RMA policy. has memory for gamers, and value stuff.
SimpleTech - good stuff. requires proof-of-purchase for RMA, so keep your invoice. less expensive than Crucial. used in servers about 10 years back.
memorysuppliers - not a name brand, but a supplier house. When you need it inexpensive. free (before 6pm CST) same-day shipping. lifetime warranty. seems to have a good RMA policy.
the memory has no company-identifying sticker, so it's impossible to trace back to the memorysuppliers for warranty purposes - write on it.
memorystock - not a name brand, but a supplier house. When you need to save even more money. web site can identify your memory (through an hta HTML application). lifetime warranty. seems to have a good RMA policy. doesn't have the higher-capacity memory.
I have not bought memory from them, but you may have a similar situation as above. probably no identifying sticker.