I've been steadily working through eBay, buying 30mm x 10mm fans, putting them on my hotend, being disappointed, and buying another brand.
The problem with most of them is that they use sleeved bearings, which means that after a couple of months they start to wear out, and sound really bad for the first 30 seconds after a cold startup.
Now I've found one that seems to work really well, it's this one:
[
www.ebay.com.au]
Gdt 12V 2Pin 3cm 30mm x 30mm x 10mm Ball Bearing Brushless DC Cooling Fan 3010B
Note that it's a ball bearing fan. It produces noticeably more airflow than the others as well, which means a cooler heatsink, so less chance of heat creep and subsequent jams when using PLA.
Very happy with this purchase