hiya! just my opinion but i would suggest progessing slower than from a finger straight to a strap on... try something more for a beginner first (just thinking of your hubby here.. a finger is nothing really compared to something bigger!)
I would recommend this: http://www.lovehoney.co.uk/product.cfm?p=8436
its brilliant and was my first anal toy.. i still use it alot now, even though i have other things for this use :-)
there are tons of things to look at and you could surprise him by buying something without him knowing - but definately start small/slim... enjoy! :-D x