There are plenty of gym in Kajang. I'll try to list them all with my personal comments.
Fitness centers(Similar concept like those Fitness First, Celebrity Fitness, etc.)
TLS Fitness Location: Sg. Chua
It's quite huge and spacious with classes. Even bigger than some of those big names. They even have swimming pool.
Rate if I'm not mistaken RM128/month (1 year contract). No joining/admin fee. Towel is provided if you are a member. Have plenty of parking space. No daily rate, but they have free 3 day trial. Short term might available but definitely pricier.
Kakigym Location: Kajang Bypass, Prima Saujana
Second largest in Kajang after TLS Fitness. They have another branch at Sg Long. Equipments might seems slightly older, but still functional.
They have many different type of packages. Normally they'll separate the fee into gym only and classes only. They do have per entry at RM10(non-peak hour), RM15(peak-hour), but need to buy at least RM50 worth of daily passes. Their 1 year contract is quite cheap. If I'm not mistaken RM800 plus 3 months free. This does not include classes.
Ghetto type:Gopi Gym Location: Sg. Chua along the main road.
Equipments are quite old, but functional. The owner will gladly be your guide in using the equipment or even comes up with a training plan for you. Largest ghetto gym in Kajang as far as I'm aware. They have more equipments compared to other ghetto gyms. No water dispenser, but the drinking water they sell is market rate. So, bring your own water if you don't want to buy from them.
Per entry is RM5. Per month is RM50.
Solid Fitness Location: Sg. Jelok
Equipments are quite old but functional. Smaller compared to They have per entry as well monthly. Per entry is RM4, excluding treadmill. To use treadmill, if I'm not mistaken have to add RM3. Monthly package includes few scoops of protein and a t-shirt. No water dispenser available. So, bring your own water or buy mineral water from them.
Caution: You might get tempted with buying steroids which they sell openly.

Stay away from steroid, especially when you are a beginner.
Four Muscles Location: Along Silk Highway. If you are coming from KL, it's on your right before Sg. Ramal toll.
Equipments are brand new. Per entry is RM8. They have packages for individual as well in groups. The group package are damn cheap but can't remember. No water dispenser as well. Lockers only available for monthly payers. They sell mineral water above market price. They do sell some supplement, brand QNT, but quite pricy.
Muscle Hut Location: Metro Avenue near Yu Hwa school.
Quite cheap but I have never workout there yet. So, I can't give more detail.
Force Fitness Location: Jalan Reko
No idea about this place.
Revolution Gym (Opening soon in September, not sure exact date) Location: Taman Damai Mewah along Jalan Semenyih
There is another gym opposite Gopi's gym. I can't remember the name and never been there.
If I missed any gym, hope others can add them as well and also update the details if the info I have given is not sufficient or outdated.
My suggestion is to try all of them before you decide the best for you in term of affordability and the environment.
This post has been edited by uvirra: Sep 12 2013, 06:40 PM