I've mentioned this before, but for annotations to
Ulysses, DON'T buy an annotated edition. I have yet to see one that does a good job because there are so many things to note. This is my personal recommendation:
http://www.amazon.com/Ulysses-Annotated-Notes-James-Joyces/dp/0520253973 . It does exactly what annotations should do--explain historical, political, linguistic, social, etc. context with little to no summarizing or analysis. If you want something more summary and slight analysis focused, use this:
http://www.amazon.com/gp/aw/d/0415138582/ref=aw_1st_sims_2?pi=SL500_SY115.
To brag slightly, but also reassure you that I know what I'm talking about, I've read
Ulysses three times in a span of four years. Once was by myself and the other two were for two different classes. The first time was a struggle, but I wanted to get out of it whatever I could with little to know help and personal research. The second time was a wash. The third time, I used those two guides and it seriously felt like I was reading a completely different book. I cannot recommend them enough.
An one last note--don't buy the Gabler edition. He added a lot of his own edits to the book. I recommend the Vintage editions. My go to test is to check the end of Episode 17. If there's a big dot after the last question, it's usually a good edition.
EDIT: Actually fixed it this time.