It's been a while since I've seen anything about future plans - and I'd like to make a few humble suggestions & comments.
Head First UML - not necessary, at least not with a UML orientation. Head First Methodologies maybe, covering RUP/UP and xP and possibly flavors of Agile. Particulary with RUP the essential question usually isn't how - but more what to use and when.....
Head First Test - everything JUnit and stuff inheriting from JUnit. With TDD thrown in for fun.
Head First Build - Ant, Maven, Cruise Control, CVS, etc. Possibly combined with HF Test.
Head First EAI Patterns - I could see (and definately buy) a small series of HF Design Patterns books covering several of the common problem domains.
Also, we're waiting with baited breath for the 'new' stuff on wickedlysmart.com, Bert'n Kathy! [ February 03, 2005: Message edited by: Don Stadler ]