For small time trading most anyone will do, but if you really go to 30+ a clip you'll have to go with an X-Trader firm, and then preferably one who has a seat on the EUREX...you'll get your fills faster and better quote stream...watch out, lots of the US firms use intermediary clearers for their EUREX business, and they pay on average 20% extra on top of the normal exchange fees and clearing.
GET a strategy for the DAX, dont just trade it, shooting from the hip, the contract volatility and tick value is high, although the Eurex has extended the hours to 22:00 now...this has definitely lowered the risk a bit.
If you're looking for Day-Trading margins the lowest i've seen is Global Futures at 2k Euro...it can help if you're going to undertake a scalping strategy and want to go in with large positions.
If you can read German (I can) check out some of the german/european chat rooms/websites about trading, search on google.de, and then use yahoo-babelfish to translate the pages for you...all the big Eurex traders are over there, Germany, France, Spain.
Good Luck...more US traders should checkout European Contracts...I think they differently played, less overplayed as compared to the US indices.