I'm quite partial to Gosling's Black Seal Rum. Had a buddy in my dorm in college who was from Bermuda who introduced me to the stuff. It's much darker than the usual range of rums, with a nice touch of molasses to the flavor. The Bermudian way is to mix it with ginger beer, but I found that mixing 1 part Gosling's, 2 parts irish cream and 3 parts milk actually made a fantastic drink. Since it was similar to a White Russian, I took to calling it a White Mongol. They were very popular amongst my friends, especially the ones who didn't drink a lot, since the sweetness of the black rum and the richness of the irish cream and milk masked most of the alcohol, yet the drink still probably topped out around 40 proof.
I had a bottle of Old Rasputin last week. It smelled like rubbing alcohol, and tasted a whole lot like Guinness spiked with vodka, only sweeter and harsher. I'd probably drink it with preference to Guinness, considering it hits like a brick. I prefer Black Toad, though, which also happens to be the only dark beer that doesn't make me feel the least bit ill from drinking it.
Also tried La Maudite, a refermented beer from some Canadian brewery that had a very dark color but tasted like a pale lager, albeit a good one, without a hint of hops. It was alright, if not to my tastes, but sure as hell not worth the $3 the bottle cost.
I like Old Rasputin, although it's kind of the Yuengling of Imperial Russian Stouts -- decent, cheap (comparatively) and readily available, but nothing to write home about. Now if you want an Imperial Stout that will ready grab your tongue and demand attention, there are three that come to mind:
The Czar (Avery Brewing, Boulder, CO) - BEST IRS EVER. I cellared mine for six months before drinking it, and it was like someone had mixed up cherry cordial and Black Forest cake and port and then distilled all those flavors into a velvety smooth reddish-black elixir. Mad love for this beer. It's also around 11% ABV and only sold in 750ml bottles, so it's a session beer -- the kind you have one of, and you take slowly.
Storm King (Victory Brewing, Dowingtown, PA)
Oak Aged Yeti (Great Divide Brewing, Denver, CO)
The latter two are technically Imperial Stouts as opposed to Imperial Russian Stouts, so they're just a percent or two weaker but still extremely full-bodied and complex in flavor (and look and pour like 10W40 motor oil).
As for La Maudite, the brewery in question is Unibroue, one of the best Belgian-style breweries in North America. We're lucky to have a several great micro-breweries in this area--Duck-Rabbit, Mash House, Big Boss, Natty Greene's and others.