The new Nokia Windows Phones (Lumia series) seems really nice, but a bit expensive. If you can get a good deal for like Lumia 710 or Lumia 800, I'd say go for it.
Androids' also really nice. I like how you can do whatever you want with them with custom installations (like jailbreaking an iphone, but better), I think I'll buy an android myself when I get the money. If you want to be able to multi-task and stuff, make sure it's a good processor in it. I think 800Mhz should be enough, possibly dual core. Quad core is overkill and it's almost impossible to use all the processor power
My current phone is a nokia x6 smartphone from a few years back, and all I can do is text and phone, so it's not really a smartphone anymore