BuddyDev

Select Blog Theme at Blog signup plugin allows users to select an available blog theme while they are signing up for the blog. It shows users the list of available themes for them and allows them to select the one they like.

Here is a screenshot

Layout Customization:-

To make the theme list good on your registration page, you may want to put the following in your css file

    ul#allowed-themes {
        overflow: auto;
        height: 350px;
    }

    #allowed-themes li {
        list-style-type: none;
        width: 185px;
        margin: 10px;
        float: left;
        display: inline;
    }

    #allowed-themes li .theme-meta input {
        float: left;
    }

    #allowed-themes li .theme-meta label {
        display: inline;
    }

    #allowed-themes li .theme-meta {
        border: 1px solid #ccc;
    }

    #allowed-themes li .theme-meta .creator {
        padding: 5px;
    }

    .theme-lists {
        clear: left;
    }