You did:-) I have been to all before and I am heading to all again in a few weeks. All are easy to do on your own and no need to pay for expensive shore excursions if you don't want to however be aware that if you are not on a ships excursion and you are late back to the ship it will not wait for you. This can frighten some people but to be honest this would really only be an issue for those areas where you are driving a few hours away and could for example get stuck in traffic.
Bergen - There are a number of places where you could dock, some are within walking distance of the city centre and others aren't however a port bus is provided and drops you in the centre (about a 5 min drive each way). You have the area of Bryggn which is all the colourful wooden houses you see when you see images of Bergen, this is a lovely area to walk around with a number of craft shops etc. The fish market is also a famous area to walk around, also free (last year anyway) toilet near the tourist information centre. Many people also like to take the funicular up the hill to the view point and walking trails at the top. This can get VERY busy so either go very early or later in the day. Sail away / arrival also involves going under what seems like a low bridge so worth being on the very top deck for this.
Alesund - This is a pretty sail in / away along some fjords. This is a pretty little town to walk around with an small tourist train which you can buy tickets for which takes you around town and to the viewpoint (the walk to this is quite a few stairs). I believe you can also book boat tours to see the birds in the local area and also in peak season they have walking tours of the town. This may be a good place to hire a car as you don't seem to be going to geiranger and this is a beautiful fjord and from what I understand a good day trip (the ship may do an excursion).
Stavanger - This is a lovely town where you dock right in the centre of town. It is a pleasant enough town to walk around with the white houses of the old town on one side of the dock and the newer town on the other. Some people do a boat tour along the Lysefjord to the pulpit rock which takes 3 hours. It books up quickly so do book in advance if this is something you want to do... Do NOT take a ships excursion for this as they charge nearly double.
Flam - Lovely fjord for sailing in / out of. Most famous here is the Flam railway which goes up to Myrdal in the mountains. Takes about 50 min each direction and most people get the same train there and back as not much at the top. Again this sells out so book in advance and DO NOT book the ships excursion as again they double the price. The ship docks / tenders depending which yours does about a max 5 min walk to the station. Last time we were here we hired bikes for a couple of hours and cycled to a nearby waterfall, this is also easily walked to and you can get maps at the tourist information centre.
I hope this helps and makes sense, sometimes my brain works at a different speed to my fingers. Any specific questions let me know. :-)