I have put some more effort into mapview.
The current version 0.5.0 has some new features which make the whole experience much more user-friendly.

In a nutshell, changes/additions are as follows:

• mapView() is now also defined for SpatialPixelsDataFrame
• all Spatial * DataFrame methods have gained argument zcol to select specific columns from the attribute table
• SpatialPointsDataFrame method has gained argument radius to scale the circles according to another variable
• added viewRGB() to render true-/false-color images of RatserStacks/Bricks (like raster::plotRGB)
• added viewExtent() to view the extent/bbox of Raster/Spatial objects. This is useful for large objects as only the four corners of the extent need to be reprojected (using raster::projectExtent)
• defined '+'-method to easily add layers to a leaflet/mapview map or combine existing maps
• defined class 'mapview' which has two slots
  • @object – a list with all objects that are shown on the map
  • @map – the map
• Raster* methods have gained argument maxpixels to avoid long rendering times (by default set to 500000 pixels which produces acceptable times on my machine)
• enhanced leaflet integration so that you can use leaflet maps and add features using mapview (e.g. +) or use mapview to create maps and add functionality provided by leaflet (using e.g. %>%)

As an example, this means that you can now do things like

mapView(meuse.grid, zcol = "soil") + viewExtent(meuse) + meuse

to view all points of meuse plus their extent on top of a raster layer of meuse.grid$soil

All new functionality is highlighted in detail in the demo at

http://environmentalinformatics-marburg.github.io/web-presentations/20150723_mapView.html

(the .Rmd source of which is now also included as a vignette in the package)

The package repository can be found at https://github.com/environmentalinformatics-marburg/mapview

To install the package use

library(devtools)
install_github("environmentalinformatics-marburg/mapview")

I hope this update will prove useful for some of you.
Don't hesitate to send me feedback and/or suggestions.

Formal bug reports and feature requests should be filed at
https://github.com/environmentalinformatics-marburg/mapview/issues

Here's an example of viewRGB()

Best

Tim