Medved QuoteTracker
QuoteTrackers main strength is its support for over 70 market data/broker feeds some of which are free. It has a solid range of charts, indicators and studies with data querying (not DDE) from Excel if more is required. Multiple monitor windows can be opened and configured with pretty much everything you would want to see including a good L2 screen. Integrated trade input is improving with InteractiveBrokers recently added. With nice inbuilt links to research, news and historical data, this application seems to accomplish a lot using few system resources. Probably the only bad point is backfilling of missing intraday data, which is inconsistent even if your chosen provider is one of the few that actually supports this feature.
Technical support is excellent with many questions being answered sometimes within minutes of mailing the support team. For many traders QuoteTracker will be a good first step.