I've written a couple of books with Packt and they are good for new authors. They pay higher royalties (avg 25%) for ebook sales, the standard royalty percentage for print copies is 15%, and it takes about 6 months to go through the whole process of writing, rewrites, and publication. Disadvantages: You don't usually get to pick your cover (They have a standard format and use photographs, so have your own photo ideas, camera ready if your heart is set on a concept), The writing can be hectic if you have a job and family on top of it, and the advances are lower than some of the other guys. Advantage: They use Word primarily, but you can give them files in OpenOffice if you want.
Bonus: They are a nice, supportive, cooperative bunch of people to work with. I'd write for them again if I had another good technical book idea ready to go.