I have this: https://www.amazon.com/dp/B00IVPU7AO/ref=cm_sw_r_awd_Ed5Wub1EQQ1VX
It's made by Samsung, and it's Class 10. I have a 32gb of the same card lying around.
This is what I use, it's a very good intersection of price and performance:
Do NOT buy from eBay, even so-called "name brand" cards are rampant with fakes. Also, don't buy a no-name brand, it's not worth the hassle. Just spend $32 on this and rest easy knowing it's fast and will work perfectly.
A comparable sandisk is fine too.
Same price on Amazon for anyone that prefers buying off of Amazon.
http://www.amazon.com/gp/product/B00IVPU7AO/
also bought this exact card 2 weeks ago for ~$38 which I thought was a good price at the time :/
great for holding a plethora of music, videos, game ROMs and other stuff, frees up the phones internal storage
Transferring files via USB from the phone to a computer (MTP) is slow (not the card's fault) a microSD to USB converter might be a good purchase as well if you plan to transfer a bunch of files at once.
Better: https://www.amazon.com/dp/B00IVPU7AO/
You can go higher than 64GB, too.
Here's what I use, Samsung 64GB EVO Class 10 Micro SDXC Card with Adapter up to 48/MB/s (MB-MP64DA/AM) https://www.amazon.com/dp/B00IVPU7AO/ref=cm_sw_r_awd_tUsTwb0J29NGS
No issues so far. I haven't tested write speeds, but it seems to be good so far.
I have the 64GB Samsung Evo which I have found to be quick and reliable. Reviews suggest that it has consistently better read and write times than the comparable Sandisk. I purchased mine from Amazon for £26.70 but its currently significantly cheaper in the US.
I purchased directly from Amazon as the market is rife with counterfeit SD cards.