What relay do I need to switch a 24V circuit with 3V
UL has tested the relay and it is capable of safely switching up to 10A at up to 28VDC (resistive load only), or 10A at 125VAC (resistive). 

According to TUV it is capable of up to 10A at 30VDC (resistive load only) or 10A at 250VAC (resistive). 

That does not necessarily mean that UL thinks the relay is unsafe at 250VAC, but it doesn't mean they think it's safe either. 

If your load is a relay or contactor (inductive load)  you had best use some kind of suppression across the coil such as a diode to prolong the life, assuming DC. If your 24V switching is AC rather than DC (as typical with a home thermostat type of system), a diode will not work and you would have to use an RC snubber or a TVS or MOV. A TVS would probably be the best choice and it should be rated to block about 35V and be of the bipolar type. 

If your micro is powered via a regulator from a 5V supply it's much better to use a 5V (or 4.5V) coil relay and drive it from a 3V signal via a transistor. Generally putting big noisy loads across your MCU power supply (such as a relay and the coupling to the load it is switching) is not a great idea. 

Also keep in mind that lifetime is only ~100,000 operations at full load. You can look at the increased life (again, for resistive load only- that's what cos(theta) = 1 means) at decreased current in the datasheet. At 1A you've got more like 700,000 operations.