Lonely Planet phrasebooks are easily some of the best phrasebooks out there (generall beating the Rough Guide ones for me). This is my second after the German phrasebook. It won't make you a master of the lingo, but it'll make you understood - the pronunciation guide is very good, and it makes Czech seem less daunting than it probably should seem.
I did find it oddly difficult to find the most basic phrases/words like 'yes', 'no', 'please' and 'thank you' though. In fact, the last one wasn't in there at all I don't think.