Not that this is strictly arcade (though there are some that have been ported on the site) I really, really recommend
Abandonia for all your Gaming From Days Of Yore needs. The site has a pretty incredible selection of all computer games from prior to 1996 and stretching all the way back to text based shenanigans that were proto Zork etc. etc. The downloads are free and it also provides all emulators you might wish for.
Any site where I can pick and choose from the likes of Zeliard, Commander Keen and Monkey Island and various Sierra outings makes me a very,
very, happy little lassie.
(Incidentally, the sister site
AbandoniaReloaded is devoted to community developed freeware, remakes and "amateur"(sp?) made games. Again, it's all free, and the amateur thing definitely shouldn't put you off, there's some absolute gems from all gaming genre's hiding on there.)
And finally, if someone can find me a pc ported version of the old TRS-80 games Dinosaur and Skiing (surprisingly one's about two fighting dinosaurs and the other is about skiing) for download and/or purchase I will fecking marry you, feed you grapes, protect you from Grues and cater to any whim you may care to dream up for ever and ever.
I shall keep myself in oysters for the rest of the week, thank you very much.