LM3914 / LM3915 / LM3916 will do this job directly. There are other ICs that will do similarly. Search for "bar graph driver".
These will interface more or less directly in place of the 2N3904 transistors in your circuit. (Just as the SSR's would that I provided references to yesterday). Some minor component changes may be needed.
NatSemi product page
Also lists I^2C only (not analog input) LP3944, low voltage, 8 LEDs. LP3943, low voltage , 16 LEDs.
IIC only - LP3943 product page
Pricing - Digikey, in stock
Note below - display can be a bar or individual dot at selected level.
Edited relevant parts from LM3914 overview. Others similar
- Drives LEDs, LCDs or vacuum fluorescents
- Bar or dot display mode externally selectable by user
- Expandable to displays of 100 steps
- Internal voltage reference from 1.2V to 12V
- Operates with single supply of less than 3V
- Inputs operate down to ground
- Output current programmable from 2 mA to 30 mA
- Input withstands ±35V without damage or false outputs
- LED driver outputs are current regulated, open-collectors
- Outputs can interface with TTL or CMOS logic
- The internal 10-step divider is floating and can be
referenced to a wide range of voltage