Chrome: There are a few excellent start page alternatives to the now-defunct iGoogle, but if you want something that mimics the look of the original, then iChrome is probably the closest option. Of course, you need to be running Google Chrome, and it's not as customisable as iGoogle, but it has a few neat functions.
iChrome gives you seven widgets: Google search, most-visited tabs, Chrome apps, traffic update, weather update, Wolfram Alpha search and news. Each of the widgets can be customised, and you can also change the background and the main Google logo in iChrome. In fact, the Google branding and functionality can be removed entirely, and you can set up your favourite search engine as the default search.
The only annoying thing about iChrome is that it requires a bit of setting up. You need to manually drag its link to your Home icon and manually set it as the default start page in Chrome settings. It's a one-time thing, but I've never seen any other New Tab replacement extension ask for that.