Big online retailer with a large selection of rums. Interestingly enough, they also sell some antique bottles, so if you're looking for a bottle of Havanna CLub 15 this might be the place to find it.
Although the nme suggests they only sell whisky, they actually offer a wide range of rums from all over the world. Shipping is fast and worldwide, and their service is good.
Master of Malt also offers a sample service that allows you to try a small 3cl bottles before buying the real thing. Intersting if you’re planning to buy $3000+ bottle of Appleton 50 for example.