Haven't been in Prague for a couple of years now, but the following site should still be useful -
Escort online - Czech girls
Also, for guaranteed professional level services (and hot girls), you can check out one of Prague's P4P institutions - K5 (
K5relax No?ní klub). I'm fairly certain they don't take commissions from taxi drivers, so feel free to get a taxi to drop you directly there. The idea is that you go in, pay a cover, sit down get a drink in a lounge area. There will be girls sitting around, dancing in the lounge. If there's one (or more) you like, ask the waiter to call them over. If you don't like anyone there, there's a fancy touchscreen thing on the table where you can call up the girls profiles. You can then ask the waiter about those.