The Eurolines bus from Tallin to Riga by Parnu leaves 2-3 differnt times each day.
The distance between Tallin and Parnu is about 120km and the last part between Parnu and Riga is about 180km.
The bus i took from Parnu to Riga was a new express bus that set me back only 12usd and I was in Riga after about 2,5hrs. It did not stop anywhere between Parnu and Riga. Bus station is located only 5 minutes walk from Rigas old town. There is a tourist information at the bus station and an a cash machine.
You can buy tickets on the bus station in Parnu as long as the bus have not left the station in Tallin. Then you have to buy the ticket on the bus.
The roads were wery good on this trip an the terrain was mainly flat without curves on the road. On the Latvian side of the border there were a lot of nice lakes in the forest.
There are regular bus departures from Tallinn, around one an hour at busy times. The journey takes one hour and fifty minutes and the cost in June 2005 was 90 Krooni.
Parnu bus station is in the centre of town. The buses we used were modern, clean and fast.
To get to Parnu, you will most likely need to fly into Estonia.
Estonian Airlines is the flag-carrier of Estonia, established in year 1992. It has flights to/from the following places (with fares that can be favourably compared with those of other national airlines) from/to Tallinn:
If You are in Tallinn and decide to explore Pärnu ( I recommend highly ) the best way to get there is by bus or rent a car. There are more than a dozen buses leave Tallinn for Pärnu daily. And six buses stop here daily en route to from Riga.
Train is also possible but there are only two trains daily from Tallinn to Pärnu.
You can take trains and buses to Parnu from Tallinn - there are several of them per day. You can also hire a car: they are not terribly expensive by European standards and Estonia can boast some of the best roads in the region.
-fast boat trip from Helsinki to Tallinn takes only 1.5H.
If you're off season try the business class...!!