哈哈哈，不好意思，没连过。

============ORACLE 8i============================
Class.forName ("oracle.jdbc.driver.OracleDriver"); 
Connection conn = 
  DriverManager.getConnection ("jdbc:oracle:thin:@myhost:1521:orcl",
      "scott", "tiger");

=============MySQL=================================
Class.forName("org.gjt.mm.mysql.Driver").newInstance();
conn = DriverManager.getConnection("jdbc:mysql://myhost:3306/dbname","user","passwd");

============InfoMax================================
Class.forName("com.informix.jdbc.IfxDriver");
conn = DriverManager.getConnection("jdbc:informix-sqli://myhost:1533:informixserver=myserver;user=rdtest;password=test");

 
============InforMix================================
Class.forName("com.informix.jdbc.IfxDriver");
conn = DriverManager.getConnection("jdbc:informix-sqli://myhost:1533:informixserver=myserver;user=rdtest;password=test"); 
=============SQLServer2000=========================
Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver");
Connection conn = DriverManager.getConnection
("jdbc:microsoft:sqlserver://server1:1433","username","password"); 
///////////////////////////////////
jdbc driver download:

SQLServer:http://www.microsoft.com/sql/downloads/default.asp
MySQL:http://www.mysql.com/downloads/api-jdbc.html
Oracle:http://otn.oracle.com/software/content.html 

---------------------DB2--------------------
---------------------  --------------------
Class.forName("COM.ibm.db2.jdbc.app.DB2Driver").newInstance();//For Application
      String url = "jdbc:db2:sample";
      con = DriverManager.getConnection(url, userid, passwd);


Class.forName("COM.ibm.db2.jdbc.net.DB2Driver").newInstance();//For Applet
        String url = "jdbc:db2:// "+server+":"+port+"/sample"; 
        con = DriverManager.getConnection(url, userid, password );

呵呵，好象已经很全了

补充oracle的连接方法：       
 DriverManager.registerDriver (new OracleDriver());
        Connection conn73 = DriverManager.getConnection
              ("jdbc:oracle:oci8:@ora8idev","scott","tiger");