Esperanto just reached the second position as the most popular language in Tatoeba, right after English. It now registers with more than 165,000 expressions and just surpassed Japanese.
Tatoeba is a wonderful reference and learning tool for all adepts of foreign languages, and for esperantists in particular. It contains over 1.6 million expressions in most known languages, and grows every day thanks to the contributions of a strong community of multilingual users.
You can use it either as a "contributor", providing translations of expressions in any language that you may master. This is a good exercise in itself and the community of users will surely let you know right away if you make any mistake. This community-based quality control has in fact proven to be very effective with this tool and most, if not all, of the translations that you will find there will be spot on. If not, feel free to provide alternative translations or post a comment for the translator with your remarks.
You can also use Tatoeba as a reference tool to look for translations of specific expressions or for examples of usage of specific words (where dictionaries usually fall short). Combined with more conventional online dictionaries such as Reta Vortaro, Tatoeba provides an excellent tool for all Esperanto learners and fluent speakers alike. I use these tools everyday in my ongoing learning of Esperanto.