Internet Drummer!   
http://www.xemico.com

This program works in the system tray and serves for checking unlimited number of POP3 e-mail accounts. It can execute various types of notifiers whenever there is new e-mail waiting in your mailbox. Each e-mail account can have its own checking interval. You can preview messages while they are still on server and decide which messages to keep and which should be removed immediately. You can set a list of spam filtering conditions and program will automatically remove such messages. You can also set a list of friendly e-mail notifying conditions and get extra notification when such messages arrive. Program also allows you to maintain a list of web pages it should periodically visit and check for changes. Whenever it detects a change on a web page you will be notified by selected notifier and/or automatic web browser launch.

X-Ray Mail Assistant Beta   
http://www.xrayapp.com

X-Ray is an email header filter and POP/SMTP server switching tool. It runs as a local POP/SMTP relay server and scans your incoming and/or outgoing mail for user specified mail headers. Once it finds a match it can change the header, remove it, replace it or perform some other special modifications. In addition, the program allows you to set up multiple profiles for POP and SMTP servers and switch between them from the system tray. X-Ray can also run as an NT service.

X-Ray Mail Assistant   
http://www.xrayapp.com

X-Ray is an email header filter and POP/SMTP server switching tool. It runs as a local POP/SMTP relay server and scans your incoming and/or outgoing mail for user specified mail headers. Once it finds a match it can change the header, remove it, replace it or perform some other special modifications. In addition, the program allows you to set up multiple profiles for POP and SMTP servers and switch between them from the system tray. X-Ray can also run as an NT service.

Simple System Tray IMAP Client   
http://www7.brinkster.com

This program includes a few interesting and useful technologies i.e. - A Simple System Tray IMAP Mail Client (not available so far) - System Tray Implementation in Visual C#.Net This includes source code, so you could use it as it is or play around with the code to satisfy your requirements. This requires .Net Framework to be installed first (I use v1.1). There is no installation required. Just copy the executable from bin\Release folder in the zip and run it. You should find the "My" icon in the System Tray. Double click to open main window. Chose IMAP Client from menu and enter user, password, IMAP Server and click Connect to check mail. Double click on SysTray icon to hide window. I made this software to serve as a personal utility for those features which are not available in the market. First one is the System Tray IMAP Client - It is very useful because I don't have to keep the Mail program open in the taskbar, there being no way to tell if there is new mail otherwise.

Ebay Auction Clock   
http://www.contactplus.com

Timer with alarms for Ebay auctions includes email notification. Unlimited number of auction items (for sale, to purchase) with support for Ebay timezone and up to 3 alarms per item. Alarms include email notification as well as multi-media file play. Runs in the system tray so unobtrusive to desktop.