Downloading Yahoo stock prices in R

This also a little late...If you want to grab data with just R's base functions without dealing with any add-on packages, just use the function read.csv(URL), where the URL is a string pointing to the right place at Yahoo. The data will be pulled in as a dataframe, and you will need to convert the 'Date' from a string to a Date type in order for any plots to look nice. Simple code snippet is below.

URL <- "http://ichart.finance.yahoo.com/table.csv?s=SPY"
dat <- read.csv(URL)
dat$Date <- as.Date(dat$Date, "%Y-%m-%d")

Using R's base functions may give you more control over the data manipulation.

Your best bet is to use quantmod and store the results as a time series (in this case, it will be xts):

library(quantmod)
library(plyr)
symbols <- c("MSFT","C","VIA/B","MMM")

#1
l_ply(symbols, function(sym) try(getSymbols(sym))) 
symbols <- symbols[symbols %in% ls()]

#2
sym.list <- llply(symbols, get) 

#3
data <- xts()
for(i in seq_along(symbols)) {
    symbol <- symbols[i]
    data <- merge(data, get(symbol)[,paste(symbol, "Close", sep=".")])
}