Capital of Austria Vienna (Wien) is wonderful historical city that is definitely worth visit and can be your next stop after Prague on the way around central Europe. The city is really easily accessible from Prague and you have many choices how to get there.
Train is truly convenient and fast way how to get to Vienna from Prague. There are nine trains going every day in different times - 4 of them depart from main train station, 5 from Holesovice. One-way ticket from Prague to Vienna costs 37,90 euros - you can get it for less (19 euros) by booking online here at least 3 days in advance.
You can enjoy nice views out of the window during the 4 and half hours long journey in comparison to bus where you would see only the highway. All of the trains stop at Pardubice and Brno, some of them as well in Kolin, Breclav, Ceska Trebova and Hohenau. The end station is usually Wien Sudbahnhof - southern railway station in Vienna with the underground station Sudtiroler Platz. Only the two night trains arrive at Wien Westbahnhof.
Second good and cheap option for getting to Vienna is by bus. Two companies provide this service - Student Agency and Eurolines. Student agency has slightly better services - you get newspapers or some magazine for reading and drink for free. It takes about 4 and half hours to get to the Austrian capital from Prague. All buses start at Florenc bus terminal, go on highway to Brno and then down to the south through Mikulov to Vienna.
Student Agency offers three buses every day departing from Florenc at 00.15, 10.30 and 12.30. You can choose to go to the station Praterstern which is located near the city center and has metro station or you can go to Vienna airport Schwechat. One way ticket from Prague to Praterstern costs 16 euros, to the airport 24 euros and you can buy it online here.
Eurolines have two buses every day - first one departs at 8.00, the second one at 17.00. They will take you to the bus station Erdberg where the metro station of the same name is located. Prices are around 23 euros for one-way ticket. Check their website at www.bei.cz.