Currently, Photoshop comes with a program called ImageReady which is the Photoshop *helper* concerning web graphics. You can do image maps and roll-overs very easily and the program is a dream to work with. This is the best bet if you know Photoshop already and if you can afford it. In any case, this is the serious path.
Actually, many WYSIWYG web editing programs allow you to create roll-overs directly, without using programs like ImageReady.
What do you want exactly, a web drawing program or a program for editing pictures for the web? The all-round solution here is photoshop, but maybe you need something more specific and a little cheaper...?