This one worked well for me:
http://microsim-shop.com/

That looks pretty much the same as the one I use as well.

Any experiences using a nano-sim in an older phone which requires a mini-sim? I believe the nano cards are thinner, and I am concerned they may not make a reliable connection. In one of my older phones the sim slot is underneath the battery, in another it must be inserted into a tray which slides into a slot.

I purchased a set of 3 that allow me to convert from any size to a larger size from here

What I like about these is the thin plastic covering on the non-contacts side of the SIM that prevent the SIM from falling out as I'm inserting it into the phone.

There are two types of micro-to-mini adapters I have seen, and I suspect both types exist for nano-to-micro/mini. I have type B) nano-micro and nano-mini adapters

Either
A) the adapter has a whole cut out, with a tiny bit of lip at corners to hold the smaller sim card, or
B) the adapter has an indention the size of the smaller sim card.

Type A does not increase the thickness of the overall resultant SIM, while type B does. Type A holds the sim a bit more securely, the lips on Type B tend to be quite small..

Type A is better for micro-mini adapters (I have had issues where the extra height causes extra wear on the sim slot pins). Type B is better for nano adapters because you want the extra material in the adapter to make up for the thinner nano sim.

I have destroyed the sim slot on a phone while using an adapter and am now very careful plus somewhat reluctant when using adapters.

Sorry for this extremely long winded reply :D

I second AnalogMan's advice to be careful with the adapters of either type because if the micro-SIM becomes dislodged you can rip out contacts when removing the SIM/adapter.

I once ruined an Option 3G stick in this manner.

Nano to micro-sim adapter are problem-prone when it must be inserted into a tray which then slides into a slot on the device (i.e. Nexus 5) as it's been known to jam the ejection port when attempting to remove the tray to swap again.

Most of the Sim card slots are not designed for frequently swapping and the contacts prone to loosening the connection over time.