depends on what u want to be doing. If you want to over clock corsair or munchkin are best brands to go with. If you dont want to spend the extra cash crushial or kingston value ram would be best for you
overclocking a Sony Vaio PCG-FX240? i don't think so for obvious reasons like it has a p3 800Mhz processor , but mostly because this is a laptop. def not an overclocking monster, i would go with the second part of XT's advice.
or if bestbuy or circuit city have memory specials during the holidays i would consider that also.
best way is to buy it from a local store in your area so you can test and if it does not work exchange or return it. than keep testing other brands. i would buy the best deal, don't worry too much about compatability as long as you buy local.
Open up your laptop and see what is in there now. You will then at least have the specifications. Then you can go look for deals that meet your specifications. I was lucky a few days ago while looking for more RAM. On the clearance rack in my local Military Store, there was a 256mb ram module that was exactly what my computer needed. Cost me $12.00