1. Gaiam Balance Ball Chair Replacement Ball, Charcoal, 52cm (Click Link to Check Price on Amazon)
Editor's Rating : 8.9 out of 10
52cm Balance Ball - Official Gaiam Balance Ball Chair BallAnti-Burst and Latex-Free

2. Exercise Ball for Stability & Balance Training, Fitness Workouts, Yoga & Pilates (Blue, 75 cm) (Click Link to Check Price on Amazon)
Editor's Rating : 9.9 out of 10
Exercise Ball for Stability & Balance Training, Fitness Workouts, Yoga & PilatesUse At Your Office - Work your "core" at the office by replacing your desk chair with a stability ball - Get fit while you work and sit at your desk - Great way to tone your abs, back, glutes, and legs

3. Trideer® 2000lbs Anti-Burst Fitness Ball/Exercise ball/Body Balance Balancing Yoga Pilates Swiss Swedish Ball trainer with Pump Plug Kit, for Pilates/Yoga/Core Cross Train/Training/Physical Therapy (Click Link to Check Price on Amazon)
Editor's Rating : 8.8 out of 10
High-quality fitness ball: Made of environmentally friendly, hypo-allergenic and articulated material, first-class processing. The ball is very hard wearing, anti-burst. Strong and Durable: With the ability to support over 2000 lbs. Durable enough to be used every day as an exercise balance ball chair for work desk office to improve your posture.A must-have training ball: The effectiveness and an almost inexhaustible selection of exercises make the exercise ball a must-have in your training repertoire. Ideal for fitness studios, for workout at home and at leisure. Ideal for yoga, pilates, fitness or simply for healthy sitting.

4. 65 Cm Anti Burst Exercise Balance Ball Extra Thick for Fitness, Yoga or Just At Home As an Office Chair at a Desk. Include a Hand Air Pump, Measuring Tape and Replacement Plug. (Click Link to Check Price on Amazon)
Editor's Rating : 9.3 out of 10
FREE - Easy to use. INFLATOR, EXTRA PLUG, MEASURING TAPE included. This professional grade anti - burst balance ball is made with durable, HIGHT QUALITY MATERIAL rated at high load capacity.WHAT YOU GET - This stability ball is best for toning and sculpting your abs, gluts, hips, thighs and more. It increases flexibility, relaxes muscles, decreases tension and aids in stretching. It enhances coordination and balance by increasing your core strength. Great for body core workouts. Try using this ball TO SIT ON AT WORK to improve posture mainly as LOWER BACK SUPPORT.

5. Isokinetics Inc. Brand Exercise Ball - Anti-Burst - 55cm/22" - Sports Orange (Click Link to Check Price on Amazon)
Editor's Rating : 9.3 out of 10
PT exercise balls are Physical Therapist quality for clinic or home use. Mix and match from our wide selection of sizes and colorsWeight-tested to support 500 lbs. of static weight. Made of special, durable latex free burst resistant material. Deflates slowly if punctured