Oh boy, you've up and done it....for years trip-hop has been my favorite genre of music and i can say that your definately on the right track with Massive Attack. Good lord...theyre almost too talented.......their classic album "Mezzanine" is proof of that alone. As for other good artists that you havent listed and that i beleive you might like.... try these..
Prefuse 73 - One Word Extinguisher
Dj Krush - Kasukei
Bjork - Telegram
Puracane - Things You Should Leave Alone
Lamb - (self titled)
Thievery Corporation - Mirror Conspiracy
U.N.K.L.E - Psyence Fiction
Dj Shadow - Endtroducing
Try all of these and call me in the morning.