Most Popular Packages by github stars:
1. IJulia: 401 stars (ipython notebook support)
2. Gadfly: 349 stars (plotting, ggplot style)
3. DataFrames: 137 stars (pandas or R data structures)
4. PyCall: 105 stars (call python from Julia)
5. JuMP: 79 stars (external mathematical programming)
6. GeneticAlgorithms: 70 stars (Genetic Algorithms)
7. Optim: 67 stars (Native optimisation algorithms)
8. Morsel: 59 stars (micro web framework)
9. GLM: 56 stars (generalised linear models)
10.Winston: 54 stars (plotting, matlab style (ish))
11.Distributions: 51 stars (probability distributions et. al.)
12.Graphs: 44 stars (graph (network) functionality)
13.MCMC: 38 stars (bayesian statistical models)
14.OpenCL: 36 stars (graphics: OpenCL 1.2)
15.StatsBase: 35 stars (basic support for statistics)