Eurolines
Eurolines is the leading provider of scheduled coach travel in Europe. It covers over 1,500 destinations in 30 countries.
The company provides regular connections between most of Europe's larger cities and Prague. Fares vary according to the time of the year and depending on how soon you buy your ticket: there are discounts if you buy it at least a month in advance, summer and Christmas time being the peak and hence the most expensive seasons.

www.eurolines.com

Student Agency
The Czech company Student Agency also provides regular connections between Prague and various European cities. The quality standards of the buses is high, and they will take you to Prague, Brno, and several other Czech towns. As with Eurolines, the sooner you buy your ticket, the cheaper it will be.
www.studentagency.cz

Connection London-Prague: both companies offer this connection in the summer season only.