Suitable graph to visualize the spread of data I have some data like
A  2
A  4
A  76
B  8
B  13
.. ....

Basically, what is the spread of A, B, etc.
What would be a suitable graph to visualize such information in R?
 A: You already got some excellent answers but let me suggest another plot that was not mentioned yet (this is an example that I created to answer another question):

In R, it is available e.g. through stripchart() or ggplot2's geom_point() or geom_jitter(). (Jitter adds a little bit of noise to avoid too much overlap.) This plot allows you to look at the data somewhat more directly than histograms (which can be badly misleading, see Glen_b's great answer to another question) or boxplots (which are great but a little more complicated to understand and explain).
In GGPlot, you can also combine boxplots and jittered dots, see the documentation.
A: As mentioned by Glen_b, there are a number of possibilities. 
Here is an example of a histogram and density plot using the "lattice" package. I've also provided some sample data.
set.seed(1)
mydf <- data.frame(V1 = sample(LETTERS[1:5], 500, replace = TRUE),
                   V2 = sample(0:50, 500, replace = TRUE))
head(mydf)
tail(mydf)
library(lattice)
histogram(~V2 | V1, data = mydf)


densityplot(~V2 | V1, data = mydf)


Both are with default settings applied.
A: There are numerous possible displays, depending on what more specifically you want. 
One example would be a boxplot for each group (A, B, ...) (assuming there are enough values in each group to support one*):
boxplot(len~supp,data=ToothGrowth,horizontal=TRUE,boxwex=.7)


But you might want to look at histograms, ecdfs, or a number of other possibilities
* Edit: from your later comments, it looks like there's enough data for boxplots.
