Actually Company of Heroes looks ideal...WW2 would be perfect (when I said modern I meant not swords-and-sorcery kind of thing). Hopefully it'll break me in gently.
I tried Red Alert 2 back in the day and didn't really enjoy it but might have to give it another try now I'm old and more patient. Sup Com does look awesome but I'm a bit intimidated by the scale
Thanks for the suggestions chaps!