As i know, every 18pins package are pin to pin compatible. the only diference will be in the internal capability (a/d, memory, USART, etc)

PIC16c622, PIC16c71X, PIC16F628, 16F819 are good choice depending what you want to do with... The best way to know what will fit to your application, see the Microchip website under the Microcontroller section OR Melabs product selector http://melabs.picbasic.com/Scripts/perl/picsearch.pl