samsung tend to be among the better ones for build quality, so if i ever had to choose a slim phone, i would choose a samsung or possibly a motorola. SE's and nokias have a habit of falling to bits.
the u600 is samsung's flagship phone, so that model is definitely not for you because lots of people have them due to the fact that they are being promoted. it's also a slider. the shine range are also sliders (or theres a candybar model). the 8801 is also a slider. i thought you were wanting a clamshell?
you could try:
-nokia 7900 Prism (its a candybar, but it looks quite unique. well, unique for a candybar anyway)
-samsung l600
-samsung s730i
-motorola RAZR Z8