I have about 2 weeks holiday, end of Sep - begining of Oct and I was hoping for your advice on where to go.
I was thinking I can visit 2 major cities and spend a week in each. right now I'm thinking Berlin would be a good option for one of them but can't decide on the second.
I'm a 27yr "girl" traveling solo. not a huge fan of museums (but do like modern art sometimes), I like modern architecture and interesting buildings. love to sit in a nice place with a cup of coffee.
I need a city with good transport system that I can easilly navigate (the tube in London was great), relatively cheap (I'm a low budget backpacker. places like Scandinavia are not for me) and finally , a city that will keep me busy for a week (I don't like to rush but don't want to get bored either).

any ideas?

www.eurocheapo.com/berlin
Paris Vienna Rome as your #2
www.wombats.at cheap stays
www.3ducks.fr if you head for Paris
www.the-beehive.com for Rome

Modern Architecture - Berlin
Sitting with a Coffee - Paris, Vienna, Rome Of those Paris has the best civic transport

Museum of modern art, cheap transportation, architecture - you've certainly chosen the right city in Berlin!

Berlin transportation can be relatively cheap, but there's quite a variety of tickets offered, so it's best to do your own research and see what works best for you. Of course, the longer period passes are cheaper than single tickets. There are cards like the CityTourCard or the WelcomeCard which will give you two or more days of limitless transportation (usually within zones A and B) as well as offering discounts on a number of attractions. Or you could opt for transportation passes only and buy a one-day, three-day, one-week pass.

Lodging: Berlin has some wonderful youth hostels. Look on Hostelworld.com, which I've found to be the most reliable hostels website, and on arrangement of the properties click on "overall rating". These are ratings from backpackers just like yourself and they will give you a very accurate picture of the hostels. I've used it several times for the few B&Bs they have listed, as well as in a pinch, when nothing else was available, gotten into a good hostel.

Of the three other cities mentioned: Paris, Rome, Vienna - I'd put in my vote for Paris.

As for cheap, the BBC News had a report that outsider are allowed to eat in employee canteens for about 5€ per meal--lunch I assume. Only the canteen of the Bundesrat and the Police Headquarters is not available. Specifically, the manager of the Berliner Ensemble canteen was interviewed and corroborated the information.

For modern architecture, Berlin, Frankfurt and Hamburg would be at the top of my list. Frankfurt has the most skyscrapers, of course, but Berlin has some really creative stuff going on with their buildings. Food is cheapest in Berlin, but really, anywhere in Germany is a fairly good bargain compared to other European countries.

For lodging in Frankfurt, try the Jugendherberge. Located on the Sachsenhausen side of the river, you have a great view and very easy access to the city sights, and lots of reasonable restaurants a couple of minutes walk away. For nature, the 11,000 acre City Forest is on the edge of Sachsenhausen, or you can take a quick S-bahn trip up into the Taunus mountains N. of Frankfurt or to the Odenwald, S. of Frankfurt. The Rhine is also less than an hour away, as is Würzburg, Hiedelberg, Idstein, Büdingen or Aschaffenburg.

Interesting cafe areas can be found on the Berger str. in Bornheim, the Fressgasse / Alte Oper area, the Schweizer str. or along the river, or simply sitting at one of the wine stands at the open produce market on the Konstablerwache or Schiller str. (depends on the day of the week)

Either Berlin/Paris or Berlin/Rome or Berlin/Madrid would provide good contrasts. All of these cities have plenty to keep you going for a week--and if you somehow do run out of things that interest you, there are a lot of interesting, easy daytrips from each of the cities.

If you like interesting buildings (but not modern), then Venice would be a possibility--lots of different influences in the architecture.