There aren't very many. The second chart here shows them. Another thing is a whole slew of adjectives that don't have comparatives or superlatives. See the list of those on this webpage, too.
The other thing you need to know is which adjectives form comparatives and superlatives with the standard endings (-er and -est) and which with the words more, very, etc. There is no magic list for those, though. You just have to know them.
Here's another chart with the most irregular: