I'm not sure if these are already in CCleaner, I'm sorry if they are. I would like to suggest:
1. Delete any index (1).dat, index (2).dat, index (3).dat, etc.
2. Delete any empty New Folder, New Folder (1), etc.
3. Leave Internet History, Autocomplete Form History, Cookies, Recently Typed URLs, and maybe Last Download Location OFF by default. Most people don't want to loose all this information. Make sure the same is done for Firefox
4. If three sounds unreasonable, provide install command-line options, or a setup config file that will define which options are on/off by default on the first run.