I've a combination of two difficult(I'm naive) requirements :(
Consider the Weather data as example. Let's say I've dataset with following information.
"Datetime", "Word", "Frequency", "Temperature"
Visualization: I want to see change in frequency of a word over time and at temperature.
- X-axis shows the time series(date)
- Y-axis has the frequency scale(0 to max freq).
Requirements:
- I need to draw frequencies of several words(Column "word") over the time.
- Correlate the frequency with temperature.
I started with ggplot2:
ggplot(TemperatureData, aes(x=timeId, y=termFrequency)) + geom_line() + facet_wrap(~Keyword) + 
  geom_line(data = TemperatureData, aes(y = temperature)) + 
  labs(x="Time Series over X days", y = "Term Frequency")
The above approach results in overlapping y axis (frequency, temperature). And, a separate bin for each "Word" (facet for ggplot). i.e plot has 3 bin's for each keyword. Each bin shows temperature over time, and frequency of a word over time.
Problems:
- I want to be able to separate y-axis for temperature, and frequency. Also, I do not want to normalize these y-axis as it gets tough to understand what are the high/low values of each axis over days. Plot Loses readability. I learnt that two y-axis is not possible using ggplot2. 
- Separate bin for each keyword is not required. One horizontal line per keyword is what I'm looking for. 
- The plot should have only one appearance(line graph) of temperature to reflect change over time. 
I tried using PAR, but could not succeed.
Example solution using plotrix package
 
    