Look at  databases at http://www.nist.gov/

The values you are looking for might not be known.  Try http://scholar.google.com/

Such a database does not exist to the best of my knowledge. There are well known standard state redox potentials in literature for a host of redox reactions. But remember, these redox potentials are precisely valid ONLY under standard conditions (1 atm/298K/1M concentration of redox electrolyte). For example, water will oxidize at 1.23 V vs SHE in acidic conditions, chloride will oxidize at 1.35V and so on.  However, these potentials serve as a reference and DO NOT serve as actual indicators of what potential your actual redox peak will appear.  "Overpotential" is the potential difference between the thermodynamic standard redox potential and experimentally observed redox potential. Overpotential data for different electrodes for specific redox reactions under STANDARD conditions is also available (to a limited extent, look it up). For example the overpotentials for hydrogen, oxygen and chlorine evolution under standard conditions with platinum electrode will be -0.07, +0.77, and +0.08V. These overpotentials result from activation, concentration and ohimic losses, and again are available only for STANDARD conditions.

There are a variety of factors that can affect the redox peak potential for specific reactions, including pH, nature of the electrode surface, electrode separation, charge transfer/diffusion rates, conductivity etc. Hence, the database that you need is more or less impossible to create for all conditions. Look into books like Bard and Faulkner's "Electrochemical methods- Fundamentals and applications" or Joseph Wang's "Analytical electrochemistry"   for detailed info. 

You may just want to look up literature specific to your research, understand your system and possible mechanisms involved, and then propose a model for what specific redox reaction each of your peaks correspond to. Comparison with control experiments are another excellent alternative. Example, if you want to find if a peak that corresponds to a particular reaction of a particular redox reagent, just have a blank solution containing ONLY that redox reagent (Known) under similar experimental conditions. Then, you may want to see if that peak position corresponds to your unknown system to confirm the occurrence of a specific redox reaction.  For example if I want to estimate whether I have a specific contaminant or not, I will just run a CV of the blank contaminant and various expected concentrations, and compare that calibration (peak current/peak potential vs concentration) with the actual CV of the contaminant containing sample that I have. 

I want to know a range for the oxidation-reduction of a contaminate to choose a suitable photocatalyst for degradation.

the values for standard condition would be a good estimation for start guess isn't it?

The reference books in the Handbook of Inorganic Electrochemistry and Handbook of Organic Electrochemistry (both are authored by Louis Meites) are common resource books for redox potentials, but I agree with Arun that that is just one piece of information.

I agree with Dr. Minteer and Arun