server.r

require(shiny)
require(rCharts)

shinyServer(function(input, output){
  output$chart <- renderMap({
    require(rCharts)
    map3 <- Leaflet$new()
    map3$setView(c(51.505, -0.09), zoom = 13)
    map3$tileLayer(provider = input$provider, urlTemplate = NULL)
    map3$marker(c(51.5, -0.09), bindPopup = "<p> Hi. I am a popup </p>")
    map3$marker(c(51.495, -0.083), bindPopup = "<p> Hi. I am another popup </p>")
    map3
  })

  output$chart2 <- renderMap({
    require(rCharts)
    map3 <- Leaflet$new()
    map3$setView(c(51.505, -0.09), zoom = 13)
    map3$tileLayer(provider = input$provider, urlTemplate = NULL)
    map3$marker(c(51.5, -0.09), bindPopup = "<p> Hi. I am a popup </p>")
    map3$marker(c(51.495, -0.083), bindPopup = "<p> Hi. I am another popup </p>")
    map3
  })
})

ui.r

require(shiny)
require(rCharts)

shinyUI(pageWithSidebar(
  headerPanel('Leaflet Maps'),
  sidebarPanel(
    tags$style(".leaflet {height: 400px; width: 800px;}"),
    selectInput('provider', 'Provider', 
      choices = c('Stamen.Toner', 'MapQuestOpen.OSM'),
      selected = 'MapQuestOpen.OSM'
    )
  ),
  mainPanel(
    tabsetPanel(
      tabPanel("thing1", mapOutput('chart')),
      tabPanel("thing2", uiOutput('chart2'))
  ))
))