Here are the results from a recently dyno tuned BMW E90 328i. The results are from the "off the shelf" flash (no custom dyno). Changes made to the valvetronic system, torque management, fueling, timing, throttle response and top speed limiter removal make for a completely developed ecu tune that was tested across many models and fuel grades (tunes are available to suit all octane levels). The gains on a Dyno Dynamics were: +14.8wHp@5200rpm & +19.4wTq@4100rpm (power to the wheels) running CA91 pump gas with no mods. This same engine is also used on E60 528i and 128i.
Each of these products is available for US$495.99 (from OE tuning dealers and ECU send in) or $695 with E-Z Flash (includes 4x map pack). More information on map switching and OBD2 flash loaders for BMW can be found here: http://oetuning.com/blog/?p=162