I've been to Khao Yai, any other national parks or other places that have good hiking areas? Maybe a day trip from Bangkok or something you could do on a weekend without spending all your time travelling there and back.

As Professor Joad would say "It depends what you mean by "near" and "hiking". I think for a general understanding the answer is NO.

THe only places that you may have a quiet lengthy walk are Prapadaeng, Rot fai Park and Buddamonthon at Sai 4.

Otherwise look at Google Earth and see if anything near enough is interesting.

There are some guys who bushwhack their own trails on the "mountain" range in Ban Chang, but it's not hiking it's...masochism. it's called geocaching

kaeng krachan NP (some 20km before cha am), khao chamao NP some 30 km after rayong (some 2 largish mountains with a trail up along the creek), also around kanchanaburi

There are some guys who bushwhack their own trails on the "mountain" range in Ban Chang, but it's not hiking it's...masochism. it's called geocaching

Yeah, I used to do that in Songkhla. We called it hashing.