Modern is usually a faster format. It is mostly lower mana curve and every single land drop counts in the format. It is also populated with many faster ramp strategies on the high end of the mana curve such as the Tron strategy that uses the 3 Urza lands or the G/R Ramp deck which commonly runs the Scapeshift/Valakut package. There are many decks that are more oriented towards the control or tempo plan also but those commonly have low mana curves as well. The main pure combo decks to look out for in the format are Ad Nauseum and Pyromancer's Ascension.
Here is an archive of competitive decks in every commonly played competitive format from Magic-League: http://www.magic-league.com/decks/