I only spent a few days in Ubud - a couple too few in my opinion, as always - but I can honestly say it's one of the places I liked most in Bali, at least of the touristic ones. Ubud still has kept it's original cultural atmosphere, and though the main road is full of shops for tourists, the rice fields and the jungle are just a few corners away.
First of all, you can't skip the ricefield walk! It's one of the typical Ubud things to do, but that has a reason. The green of the ricefield is just hypnotizing, and depending on your motivation and curiosity, you can detour your walk as far as you want. If you feel thirsty, get a coconut fresh from the tree offered to you by one of the kids on the path. Pay attention to the beautiful partnership between ricefields and jungle on your walk, and the natural way one flows over into other.
Apart from the stunning landscape of rice fields changing with pieces of jungle, there is a lot more about this place. In the early morning (as early as 5Am, Balinese are morning people!) painters come here to fill their canvasses with birds and flowers. Many other artists, e.g. woodcarvers, have their little workshop located near the paths. I met a very talented one, Kadek, who has his atelier on the path that is leading to Ubud from Sari Organik, the must-visit organic restaurant I will tell you about later. He carves his masks directly where you watch, from light hibiscus wood with its beautiful patterns. I could not resist of getting myself a mask - Hello, tourist in me! - since they were one by one beautiful. His name is Kadek Astama, if you ever walk by - admire his work and tell him I said hi! :)
So, more about Sari Organik - it is one of the best organic food places in Ubud, located in the rice fields as I metioned before already. They have their own farm, where you can buy fresh vegetables, herbs and fruit as well. I was sincerely surprised by the exquisit taste of the plants in my salad, half of which I had no idea of what exactly they were, but delicious is an understatement. Another recommendation is the "tofu falafel" pita, I never knew tofu could taste THIS good!
Since you are visiting one of the biggest cultural centers of Bali, you should soak up some culture, by going to a traditional dance performance for example. There is a daily performance by different companies in the Ubud Palace - which are quite good. Especially the elaborated costumes draw the attention, and the special mimic and eye-movements of the performers. You will never find any local at these performances, but this has a logic explanation: these dances are originally performed at festivities and festivals, so every Balinese sees them once in a while already.
And, one of the biggest 'attractions' of Ubud, The Sacred Monkey Forest. Nothing too much sacred about, just a forest full of annoying, yet quite cute monkeys in my humble opinion. I am an animal lover, so I couldn't have skipped it, and 20000 rupiahs poorer and my camera almost glued to my hands, I entered this enchanted forest.
First of all, I highly advise you to not take ANYTHING of value in there, no open bags - if possible no bags at all. Those little bastards will try to lay hands on whatever they get! if you're brave, you can try sit next to one of them and hope they'll hop on your lap - but the guy that did that, and enjoyed it for a while, almost ended up bitten by his little 'friend', so I decided to not even try it. Even though trying to avoid them, eventually I got in a fight with one of them, when I was visiting the temple and the little bastard tried pulling off my sarong. I did feel a bit afraid when he started to pull, since another one joined this fun game, and they kept on following me so I even didn't dare to turn my back. Luckily, when I decided to fizz at them like an angry cat, they changed their mind.
The cutest thing are the little ones, clinging on to their mom. Most of them are just sitting, eating fruit - or fleas, or just looking on what to steal. No matter when you'll go, you'll surely witness someone getting robbed, 200% guarantee! To get your stuff back, you can try asking help from one of the workers, but to be honest, it's quite a hopeless case, so just make sure to really take the warning serious and not take anything 'stealable' with you. The temples inside are quite nice, and you can rent a sarong for a free donation - just like in many other places.
Ubud is also the place to be if you want to take some language classes, or for practicing yoga, going to a healer... It's actually one of the most provided cities on Bali, where you also find the most expats, as a logic reason. I personally didn't have time nor energy to explore the nightlife, but it seems to be cool as well.
Critics say it's too touristic to represent the pureness of Bali, I personally think that if you choose the right places and activities, it's a wonderful place to stop for a few days before going into the wild!