Walther P99 and PPS. Doesn't get any easier.
I don't think that you'll find anything easier to break down than M9/92-Series.
IMHO Glock is the easiest -- Springfield XD, Beretta, Sig, CZ are also easy. 1911 is a PITA the FIRST TIME -- gets easier. Have no experience with any Ruger or S&W semiautos.
I have owned both berettas and glocks. I believe berettas are the easiest to disassemble, clean, then reassemble. just make sure you have it pointed in an upward angle when you disassemble. glocks are also fairly e-z to do same.