Janis Elsts

Normally when you login to your blog WordPress will create a session cookie that is used to authenticate you. If someone was to steal the cookie they would be able to use it to get full access to your blog without having to know your password. This plugin prevents that from happening – it makes the cookie specific to your IP address, so it won’t be usable from a different computer.
Use this plugin if you have a static IP. If you have a dynamic IP address and it changes often you will get logged out frequently.
A bit more info can be obtained from the <a href="http://w-shadow.com/blog/2008/07/12/safer-cookies-plugin-for-wordpress/" title="Safer Cookies homepage" rel="nofollow ugc">Safer Cookies homepage</a>

Safer Cookies

Ties the WP session cookie to your IP address so that it can't be used to get access to you blog from another computer.

curlybracket

This plugin creates a widget which will show the title, thumbnail and link to the last 5 posts a user has consulted. 
To store the data it uses sessions.
Session handling is provided by slightly modified functions from the simple-session-plugin by pkwooster.

Last Seen Posts Widget

Show title and links to the last 5 posts a user has consulted.

Safer Cookies vs Last Seen Posts Widget