Sometimes the smaller robotic kits like the LEGO Mindstorms NXT kit just aren't enough. The Lego kit by far gives the best bang for your buck. But being a robot enthusiast and buying several kits now they have gotten bigger and more complex
If you are looking for big robot kits you can check the Robovie-M V3 (Big-Max) Humanoid Robot Kit. It retails for around 2700$.It is currently the hottest Humanoid Robot in the market for research institutes and the battlebot world. It is designed with a strong and well-balanced body kit. Robovie-M V3 has a total of 22 joint angular sensors, it is capable of doing basic moments, throwing objects, punching, somersaulting, doing handstands, side stepping, and playing soccer with other Robovie-M V3s. When it falls, it automatically pushes itself back up to a standing position. It comes in 2 stylish colors and a full metal body outfit. It includes 70 predefined programs.
If the price tag is a little outside of your budget like mine was when i first started you can try building one on your own. If you are a noobie to electronics there are a few really great books that i have bought myself that provide step-by-step instructions on how to construct a small robot that is programmable from scratch and spare junk electronics around your home. "Robot Builder's Bonanza, 4th Edition" and "Robot Building for Beginners" books are excellent.
If you are not interested in learning about the electronics and just want to focus on the programming aspects then there are a bunch of moderately proceed products out there in the 200-500$ range as well. By far though the LEGO Mindstorms NXT kit is by far the best. It provides great flexibility due to how the lego bricks are constructed and is designed for a noobie programmer. There is tons of online support and even a community of lego programmers. They will be issuing an updated kit soon likely in 2011. You can construct a fairly large robot from the lego materials and purchase more for a very low cost to add to the kit.
If you are looking for a great place to buy beginners, intermediate or advanced robotics kits then you can get great deals at Amazon