many people out there will suggest GWX 1.03 (myself being one of those people who would suggest it) or you could wait until GWX 1.04 comes out
hopefully soon 
also...
SH3 Commander is an important one to have
SH3 Weather fix
Open Hatch Mod
thats pretty much the four main ones i run with... of course there are as many mods as there are play styles. there are also a lot of skins, and a lot of new mods i havent even had a chance to take a look at yet.
to recap, if you nab GWX 1.03 with SH3Commander, Sh3 Weather fix and the open hatch mod, that would be a good starting point for you.