I'll give you a little Rock/Metal ----> Rap/Hip Hop primer.
First, I'd say avoid Death Grips at this early stage, they may put you off for life. A REALLY aquired taste (sorry TW, as someone who likes a hell of a lot of Rap, I really don't like 'em, strikes me as Rap made by a dude who can't rap for people who don't actually like Rap, in my humblest of opinions - and I have given them a decent crack of the whip).
Now that, that's out of the way.
Start with something like the Judgement Night soundtrack if you don't already have it. Rock/Metal/Alternative acts collaborating with Rap acts. Song structure is very traditionally Rock, nothing too heavy in the rapping, and a variety of styles of rapping from more traditional/old skool Run DMC, through Del The Funky Homosapien, via Sir Mixalot, up to the more aggressive style of House OF Pain, Onyx, Boo-Yaa T.R.I.B.E. etc . It's a good primer and halfway house between Rock/Metal/Alt and Rap and covers a lot of bases.
Maybe move on to a bit of Beastie Boys. Start with Ill Communication as it has Sabotage on it and everyone loves Sabotage deep down. Again, more traditional songwriting and structure. Plus live instruments and non threatening white guys. Then maybe move backwards to Check Your Head and finally Pauls Boutique to delve into a more hippity hoppity sound.
Another "gateway" album has to be Cypress Hill - Black Sunday. A lot of "gangsta" shenanigans (drugs/violence/guns) but delivered in a more accessible way than if you were go straight for something like Wu Tang or whatever. Song structure again, quite traditional and some familiar samples (spot the Sabbath samples). A good intro to a slightly harder edged lyric, but delivered with humour and that delightful B-Real whine.
As suggested earlier Dr Octagon - Dr. Octagonecologyst is a great example of everything just clicking. Great (and unusual) production from Dan The Automator and a masterclass in turntables/scratching from DJ Q*Bert all wrapped around some very darkly humourous raps from Kool Keith. Utterly essential.
I'd also say give Gravediggaz - Niggamortis (known in the US and later Euro releases as 6 Feet Deep) a whirl. Again, darkly humourous lyrics and a bang up production job serve up another essential album. I could listen to this all day and not get bored.
I think they're probably the easiest starting points. Not too much "gangsta/kill whitey" stuff, familiar song structures for the most part, and some great lyrics.
Don't be put off by what you may percieve Rap lyrics to be all about. It's not all money, guns and bitches. There's a lot of positive stuff out there, a lot of very clever word play, and some really dark stories out there and all sorts of other shit in between, just as with the different flavours of Rock/Metal. Dip in to the above and hopefully you'll find something that you like and we can tailor more suggestions from there I reckon.
I mean I could have trotted out Public Enemy, NWA, DMC, De La Soul, Black Sheep, Wu Tang (and associated) etc. etc. but coming from a strictly Rock/Metal standpoint I think you need to acclimatise and get a handle on what sort of Rap you like before we go too deep into the "classics".