Lots of useful links.
From a Sketch to Illustrator
This website has some some great tips about how to create a Illustrator image when starting from a hand drawn sketch.
Technical Illustration with Illustrator
This website has some tutorials about how to create technical looking drawings using Adobe Illustrator. Going through these tutorials will help you get more comfortable with the pen tool as well as others.
Illustrating an iPod
This tutorial video will show you how to illustrate an iPod using techniques in Illustrator. It has some good use of gradients to make the iPod appear three dimensional.
Smashing Magazine's List of 60+ Logo Design Tutorials
This list has a lot of interesting tutorials on the process of logo design. Some of the tutorials show how to make a specific logo in Illustrator, and these would be good tutorials to do for more practice in Illustrator.
This tutorial explains Illustrator brushes, which weren't covered in these tutorials. However, this tutorial will introduce you to how/why to use them.
Good-Tutorials has a large variety of Illustrator tutorials on how to draw specific things. If you practice on these, you will learn different techniques.