Hello,
any character based LCD display from Conrad is OK. All those modules use the same controller chip HD44780 and you can find the routines for this type of LCD on any PIC Web page.
Those relatively cheap modules are character based. It means that they have a fixed character set which can be displayed and also they have couple of user-defined characters.
Those modules are available in various sizes like 1x16, 2x20, 4x20 etc. First number is number of lines and second number is the number of characters per line.
Graphical LCDs are different, more expensive, but you can address any dot on the display, so you can for example draw a circle on LCD.
I would recommend that you should start with some cheap character based LCD. For example 2x20 is nice, you will have two rows of informations, 20 characters per line.More than enough for debug messages, user input etc.