Here is a good collection of weekend trips that you can take from Bangalore. Most of these places are less than 200 kms to keep travel time well less than 4 hours including city traffic. The general tip that I can give however is to leave as early as possible from Bangalore so that you avoid city traffic.
1. Nandi Hills ( < 100 km from Bangalore)
Start from Bangalore towards Bellary road and reach Devanahalli cross. The road is really good now and you can make it within 20 min from Hebbal any time of the day. Take the deviation on the left and travel 11 kilometers to reach Nandi cross. This road is not the best and make sure you dont miss it. On the Doddaballapur road, turn right to reach the road that leads to the top of the hill. You need to travel about 9 kms with 17 pin bends to reach the top.
Apart from tippu drop, there is ample space to sit and laze around. The best time to go here is during October - January which is peak winter. Otherwise any other day when you feel the weather is pleasant. Early morning should be the best time and you may not be allowed to stay beyond 5.00 pm there.
2. Mysore
Needs no introduction. There are enough places to see here in two full days. The ideal trip to Mysore should include 2 evenings; one of Brindavan gardens and other for the palace. Know that the palace is lit only on weekends and during Dushera.
3. Belur , Halagidu and Sharavandabelagola.
All the three places come within a 65 km radius and the best place to stay would be hassan. Hassan has a good number of hotels to stay and its also reasonably priced. Also Hassan should be a good place to return to at night if you are not able to complete all three places at one go.
It might happen that you will need more time, that too if you are like me who want to take snaps of all the scuptures in Belur and Halegidu. Shravanabelagola might not take more than 2 hours to see as it is a small place.
The best time to visit this place is again winter becuase there is not much share in belur / halebidu and the whole experience can go wrong if the day is too hot.
A list of not so good places.
This is the list which I personally wanted someone else to give me. Out of my experience, a lot of near to Bangalore places mentioned in so many websites are in reality not worth it. The reason may be because the place itself has lost its glory, or is seasonal. I have made it a good point to mention the best time to visit the place whereever I can.
Some people may differ with the examples I have given below. Please feel free to comment on this and I will add yours along with your name/bloglink if you want to add few more
1. Bannerghatta National Park : ( < 35 km )
I remember having visited this place so many times in my childhood. I have been here recently and dont feel there are enough animals (or at least I did not see many) to call it a National Park. My friends still argue that the Safari is worth, but I could spot only a single bigcat during my trip. There is no scope for night safari either that makes this less interesting.
2. Charles bandi : ( < 90 km)
This is an old fort cum garage (if i could call this). This was supposedly a collection of previous generation vehicles from mass people carts, hunting carts, some very old diesel vehicles, some old mass transportation system, etc, etc. This seems interesting, but unfortunately there are only a few of these vehicles.
For people who still want to try, this place is about 20 km from Channapatna on Mysore Road. Take a deviation on right about 5-6 km after crossing Channapatna towards Mysore and travel about 15 km and ask for mogenahalli.
For me first it was difficult to find this place and then I felt it was not worth it.
3. Big Banyan Tree OR dodda alada mara ( < 100 km from Bangalore)
The tree is really big and astonishing. But make sure you plan something else along the way like Mysore or Srirangapatna. You may not need more than a couple of hours to spend there.
This is it, please comment on this and let me know what you think are the additions.
