merge 3 data.frames by column names

You can use the Reduce function to merge multiple data frames:

df_list <- list(DF1, DF2, DF3)
Reduce(function(x, y) merge(x, y, all=TRUE), df_list, accumulate=FALSE)

Or merge_recurse from the reshape package:

library(reshape)
data <- merge_recurse(df_list)

See also the R Wiki: Merge data frames

After researching this very same question for a couple hours today, I came up with this simple but elegant solution using a combination of 'dplyr' pipes and the base R 'merge()' function.

MergedDF <- merge(DF1, DF2) %>%
              merge(DF3)

As you mention in your post, this assumes that the column names are the same and that there's the same number of rows in each data frame you are merging. This will also automatically eliminate any duplicate columns (i.e., identifiers) that were used in the merging process.