Microsd (SD= Secure Digital) cards are becoming more popular as the day goes by, don't you think so? Think about it. Even Sony Ericsson has stopped using their proprietary M2 memory cards and went all out to support microsd cards in their latest Sony Ericsson Satio mobile phone. I think more SE mobile phones supporting microsd will be released by Sony Ericsson.
Having said that, there are so many brands and capacity of microsd cards available in the market right now. Being the smallest memory cards available in the market right now, it is important to choose wisely. MicroSD cards will support a capacity for up to 2GB. Anything above 2GB will be identified as MicroSDHC (HC=High Capacity). Presently, the largest capacity for MicroSDHC will be 32GB. Newer gadgets especially new mobile phones will be able to support MicroSDHC although the newer mobile phones will still be able to support lower capacity MicroSD cards.
There are mainly three type of speed ratings on any microSD/MicroSDHC card. It goes by Class 2,4 and 6. Basically Class 2 will give you a theoritical 2MB/s access speed (or more commonly known as 13x), Class 4 will give you 4MB/s access speed (or more commonly known as 26x) and Class 6 will give you 6MB/s access speed (or more commonly known as 40x).
Non MicroSDHC cards were based on the old SD 1.x specification. MicroSDHC cards, however, are based on the newer SDHC 2.0 specifications. It is vital that you understand the maximum capacity which your mobile phone or gadgets can take. Never buy a higher capacity memory card if your device could not support. It will be a waste of resources.
There are many manufacturer who are offering MicroSD/MicroSDHC cards for sale. A typical household name will be Scandisk, PNY and Toshiba. They are reliable cards to use. A typical reliable card will offer 5 years limited warranty. Make sure that you hold on to your receipts after you have received your goods. You never know what's going to happen to your card in the future (just in case it breaks down).
Good luck in searching for a good memory card! By the way, I have a picture of a Toshiba 16GB MicroSD card which I have purchased lately for my Nokia E72. I got it for around £32 on ebay. It is a bargain! I have looked elsewhere and they are selling a tyical 16GB Scandisk MicroSD card for £45!