Literally most any PIC you pick will do. I search MChip's site for the flash units with 2 or more A2D's (the lowest count is will search for) and got back 166 of 186 hits. Even the lowly PIC10F220 (the tiny 6 pin SOT device) has flash memory and A2D

Microchip search page:
http://www.microchip.com/ParamChartS...g=en&pageId=74

Just keep in mind the A2D converted can only range up to it's reference voltage (which is fixed to be VCC in the 10F220), so you'll need a voltage divider to being your 24V down to the range the PIC can read. That divider is also a nice place to add some overvoltage protection too.