How do I prevent tomato making quiche soggy
You may wish to seed the tomatoes, removing the gelatinous part containing the seeds, which is mostly water, and very little flavor.  You want to use only the meaty, fleshy part of the tomato in a quiche.  

Depending on the size of your tomatoes, scooping the seeds out with a melon scoop, cutting out the seed sections, or simply squeezing out the seeds will help.  The Shiksa in the Kitchen has a very nice article with very clear pictures showing these three different methods of seeding tomatoes.

This will substantially reduce the amount of moisture the tomatoes are adding to your quiche.

Another method you may choose to use, if you have the time, is to roast your tomatoes before using them in the quiche (which may also involve seeding them first).  This will reduce the moisture and concentrate the flavor.