Travel tips (Katowice, Gdansk, Krakow, Zakopane, Warsaw, Wroclaw, Sopot)

Hi,
I'm looking at spending a month in Poland in September / October 2012.
My intention is to fly into Katowice, spend a month travelling around and then fly out of Gdansk.
I did something similar 5 years ago, using busses & trains and visited Krakow, Zakopane, Warsaw, Wroclaw & Sopot.
Can anyone recommend any 'must see sights / places' that I can build into my journey.
I'm on a budget, but flexible and very adventurous!
Many Thanks
A

This time, skip Sopot and spend some time in Gdansk. The Old Town is beautiful but there are other places to see and things to do here.

for example a brand-new, shiny, southern beltway of Gdansk ;)

Actually, I was thinking of Westerplatte, Oliwa Park, the hill behind the main train station, the Solidarity museum, and many others.

Thanks guys, I failed to mention that I have visited Gdansk on another trip, I was thinking this time, maybe heading to the 5 lakes area - any advice?