You can use http://qype.de for information on bars / cafe / etc in some areas and if you are for more biz related things, I suggest you give http://xing.com a chance and search the forums for the name of the town - several of the areas are very active, I think the munich group has nearly 30K members.

Be careful that some areas are namend after the region, so not necessarily frankfurt but rhein-main-gebiet or so.

I mention Xing because while you do come over not strictly for business, these groups often have meetings and local knowledge and might help you with.

Even thought the language is set to german, you might get away with writing english and even receive some answers.

As for showing you around, not sure what you want to achieve, but nearly every german site has tourist bureau / website which should provide you with a lot of information.
hth