Online ad networks and ad-serving companies consolidated this year, leaving the market with a small group of strong players: CMGI, DoubleClick, 24/7 Media and Real Media. CMGI led the acquisition movement, rounding up ad-serving companies including AdForce, AdKnowledge and Flycast Communications Corp. DoubleClick, meanwhile, acquired rival ad network NetGravity and Abacus Direct Corp., which markets consumer-buying data to catalog companies. That left Real Media and 24/7 Media as the remaining major players. Previously focused exclusively on repping a network of newspaper sites, Real Media reorganized to include sites for travel, personal finance and other vertical segments, a move that positions it squarely in competition with DoubleClick, 24/7 and CMGI's ad networks. Consolidation may not be over; while 24/7 is mum, industry insiders bet CMGI or DoubleClick will buy the network.