Where to go from Helsinki?

You won't believe this, but when I was last there on business, I found a 100Euro flight from Helsinki to Rome on Finn air! Got it through expedia.co.uk. You might want to see if you can fly to Helsinki, and then out of a different city so that you can extend your days and not chew them up traveling.
Last but not least, check out the ferry to Estonia and Latvia, which is where the locals go to spend $$. The VAT in Finland and Scandinavia is around 24% along with the high costs. "Economically" is a seldom used word in that area!

Do you have to fly home from Helsinki? Or can you get a flight from your new city, to home?

I'm waiting to see how Randy pulls this off since I might want to piggyback.

My bet is either/or.

Scandinavia would be: Stockholm -> Oslo by train, Oslo -> Copenhagen by ferry and train.

Hard to do in a week.

Yes Ed, there are too many viriables here until we know if Kelly has to return to Helsinki. If not, it would also help to know if s/he has a preferred city to fly home from. If it were me, I would try to identify the most economical open-jaw flight among 3-4 likely cites, get the ticket and then plan the week with that destination in mind. Without that information, it's kind of like shooting darts in a dark room.

Of course, if Kelly is willing to jump through the Visa hoops, a round trip to St. Petersburg and a couple of day trips from helsinki would easily consume a week.

If you want to go to St. Petersburg, you should be applying for your Visa right now. You must do that before you leave the U.S., and there can be delays. I'd recommend using a reliable agency to do it. Since Helsinki does not have an "Old Town", a trip to Tallin via ferry is great.

Thank you everyone for the suggestions and input- I am fairly unfamiliar with this region of Europe, so it is great to get input from people that have been there!
As of right now, we are open as to what our return travel plans are- our flights have not been purchased as of yet, so we can leave from wherever we choose.

I was looking into the visa issue last night and it seems like quite a lengthy process... would it even be possible to get that done before May 1st?
I hadnt even thought about air travel around the area- I have been primarily focused on Eurail as that is what I am most familiar with. I will definately look into air travel options.
I am very interested in the overnight ferry to Stockholm and I did notice that we could do a speed boat from Helsinki to Tallinn and then overnight ferry to Stockholm- Is Tallinn worth the day trip?

OK Kelly, Now that we know you can fly out of anywhere within reason, I would suggest one of two options depending upon the VISA question;

1) Apply for VISA ASAP for a 2-night stay in St. Petersburg. Use one of the services that expedite this for a fee (not my area of expertise). Then return to Helsinki and do a Tallinn day trip (early boat there, late boat return is plenty of time to see the old town). Then take the overnight ship to Stockholm and spend 3 days there & fly home. (or boat Helsinki-Tallinn-Stockholm - see below). That's a very nice, multi-cultural week.

2) Omit St. P. and it's VISA problem. Do the Tallinn day trip but make it a one-way boat trip. That evening, catch the overnight ship from Tallinn to Stockholm (I seem to remember this as an option, but not 100% sure - if not, return to Helsinki next and ship from there). Spend 3 days in Stockholm. Early train to Kalmar, Sweden to see the cute town and castle (3-5 hours) - late train to Copenhagen. 2 days in Copenhagen. See Frederiksborg Slot (castle) while there - a short train trip out of the city. Fly home from Copenhagen.

There is not enough time to do Norway, even quickly, unless you skip the other countries and fly direct to Oslo from Helsinki (SAS economy fares are good). From Oslo you could head toward Bergen over 4-5 days and have a nice fjord experience. PM me if you want Norway options.

Good Luck!

Taking the ferry to Stockholm and Tallinn is a wonderful idea. Stockholm is one of the most beautiful cities in Europe. Tallinn has a very neat and interesting old town. If you can only do one, I would pick Stockhom because it has a fantastic old town too.

We went to Helsinki when traveling around before starting a RS Scandinavia Tour.
Stayed a couple of nights in a college dorm (cheap). Took the high speed ferry to Tallin and stayed there 2 nights. I would never pay for the high speed ferry trip again. The regular ferry is almost as fast and doesn't bounce around like the high speed ferry did. We then flew to Stockholm for a couple of days before our tour started. Next time: take the ferry to Stockholm and see St. Petersburg when getting that close to it. Almost everyone I have talked to about that trip said I should have skipped Tallin and gone to St. Petersburg. Next time......

These are all cities on the sea- take a boat! You will enjoy the travelling so much more than you would by train. The ferry (that's a nice ship) from HKI to St.Petersburg can be found here: http://stpeterline.com/en/
Tallinn is also less than a hour by a hydrofoil boat from Helsinki and it has a nice old town right close to the harbor.
You can take a ferry (maybe 16 hrs) from HKI to Stockholm, or to see the most of a fabulously beautiful archipeligo, take the train from HKI west to Turku, Finland and then hop on a boat (Silja line http://www.tallinksilja.com/en/schedules/helSto/default.htm or Viking lines). Re: discounts for Eurail card http://www.tallinksilja.com/en/tab1/oneWay/eurail/

So, as we get more and more details from my husbands corporate office, I now have a more distinct shape to our trip. We will only have 5 days to travel between Helsinki and Copenhagen (which is where we are flying out of)... i am thinking of doing a day trip to Tallin, overnight ferry to Stockholm for 2 days, train to Kalmar for a day and then train to Copenhagen for last 2 days... Or Helsinki to Stockholm (skip Tallin) train to Oslo, ferry to Copenhagen...
Any thoughts as to which is the better plan?

I think either of those plans would work, Kelly. If it were me, I would go with the first one because I think the transportation would be a little easier. Also, I am not a huge fan of Oslo (though there are some interesting things to see), and I loved Tallinn.