firstly i'll throw out there that i have no interest in stock quotes or anything of that nature. i will, however, try to answer this post with the best of my knowledge on basic information that i know about web queries and excel formatting.
as far as i know, microsoft excel has built-in web querying (excuse my typo's.. its late and im still at work). I know for a fact that the windows version does, but it's been some time since i've used the office package on os x. Lets assume it does.
Open a new workbook. Click Data and then go to Get External Data > New Web Query. A window will populate and a few necessary fields and radials will be available for you to mess with. The first field is for a web .csv location that most stock sites will export data to. (if your unfamiliar with .csv its just an extension for comma separated values with text documents store data with comma separating each value to easily be imported into databases like excel or access, but if you already know that .. then cookies for you). I used yahoo.finance.com for most of my attempts and doing this. Look up a stock quote and look for a link called "Download Data" copy that URL into that field, one should look roughly like this..
http://download.finance.yahoo.com/d/quotes.csv?s=ASD&f=sl1d1t1c1ohgv&e=.csvI typed in "ASD" into the search function.. i have no clue what this company is.. it was just blind left hand typing.
plug that guy in there.. leave the rest of the radials the way they are and just hit ok. You can come back and mess with those settings again later if you want to play around. the next window is basically where the information will be located on the spreadsheet and if you click properties... you'll see refresh options to keep your data updated. its lowest interval is a minute.
After you apply the settings.. youll have a single cell with a comma separated value format to it.. to expand the information accross separate cells .. click Data then Text to Columns. Choose the radial for Delimited, click next.. put a Check in Comma and then Next & Finish.
Wee.
Now.. if you want multiple queries.. make new sheet/tabs for each. I don't think you can have more than one quere per sheet. And if you want eyecandy that all the bored excel people like.. you can just have one sheet be the main and have it update from the other sheets into your main..so you can look at all the information for several quotes all at once. if you know excel, then this should be cake.
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now.. to answer your question about plugin's or 3rd party apps for excel .. i couldnt find any at versiontracker or various other places. this was the only way i could come up with using excel.. there may be someone out there that knows way way waaaiii more than me about this subject. getting real time quotes.. i found widgets and other various apps .. but none for excel.
good luck.