If you make it to Estonia, you MUST take the ferries to the Islands of Muhuu, Sareema and Haapsalu! (Forgive my spelling - and I have no excuse: my Missus is Estonian and we've only been married 9 years!) These Islands are other-worldly for their beauty and history - I can remember massive castles, huge lighthouses, windmills, beautiful lakes and a massive crater where a meteorite landed thousands of years ago. OK have a beautiful blue-eyed blonde Estonian chick with you probably helps you see things through rosier-tinted spectacles, but these Islands really are something else! Also go to Parnu, the summer beach resort; sun, sea, sand, surfing, wind surfing, health spas...need I say more? It is about a two hour drive from Parnu to the city where you catch the ferries to the Islands - if you are interested I will ask my wife its name. I can also recommend a very good tour guide for you - my brother-in-law! Tallinn is, of course, a must see - but not a great place to drive; ancient streets, some quite bad roads and some not very safe suburbs if you wander off the beaten track. I would say stay in a cheaper Estonian Hotel (Tahertorni springs to mind) with safe, guarded parking, perfect English speakers and take the taxi into and out of town.
If you go further east, Narva on the border with Russia is worth seeing and there is also an off-road driving adventure near Johvi (in an old mine, I believe), guided kayaking on easy rivers, beautiful freshwater lakes...
But - be aware: there is poverty you would not believe, lots of old communist buildings, lots of Russian mafia and places to avoid...
If in doubt, hire my brother-in-law!