As with Deadliest Catch (see below), you'll need to fish up a raid boss for this one, but fortunately the Lurker is a lot less annoying. There's no additional trip required to pick up a special lure, although you will need to be able to survive some hostile waters long enough to reach the Lurker's platform. However, at 80 this shouldn't really be an issue because the Coilfang Frenzies in the SSC waters are only 70 elites.
Head to Serpentshrine Cavern, take the big elevator down into the instance, and then take the small elevator up to the raid's starting platform. At this point, you can either drop down to the water below or you can stealth your way to Lurker if you're a stealth class. His platform is located smack in the center of the raid, and you can swim over to it (assuming you can survive the Frenzies you may aggro), use either a water-walking or levitate effect to reach him, or stealth (then swim) over. The big, circular platform in the middle is the one you want.
At this point, you'll want to take all your gear off, because there's no way to survive Lurker even at 80 in tank gear (trust me on this one). Safely naked? Start casting your line into the central pool and just keep fishing -- eventually, Lurker will appear and you'll have your achievement.
Old Man Barlowned
Easy -- it just takes a bit of persistence. Keep visiting Old Man Barlo at Silmyr Lake (northeast of Shattrath) each day until you've picked up -- and successfully completed -- each of the 5 fishing dailies he offers.
This one's pretty easy at 80, but can be a bit time-consuming if you don't already have a few Mudskunk Lures lying around. These are items (that, interestingly, are not soulbound, and can thus be sold or traded between characters) that can be purchased from Nat Pagle on a small island at 58, 60 in the bay of Dustwallow Marsh. You'll need at least one to do this achievement, and if you plan on spending any amount in Zul'gurub farming rep or mounts, it's usually worth your time to pick up a bunch at once.
Got at least one? Head to Zul'gurub, and once inside, drop down to the river circling the north-central part of the zone. If you have Find Fish, you should see a few Zulian Mudskunk pools pop up (although they are technically named Muddy Churning Waters). You'll need to fish up 5 of these. Once you've got them, you will now able to summon Gahz'ranka.
At this point, all you need to do is swim to the northeastern bend of the river to Pagle's Point, climb ashore, and right-click your Mudskunk Lure. As soon as Gahz'ranka appears, you should have your achievement.
The Coin Master
I have gone on record several times before saying how much I love the Dalaran fountain, and I'm tempted to devote an edition of the OverAchiever to the lore behind all of these coins.
Sadly, the meta-achievement linked to them is another big pile of RNG. There's no real strategy to be had here; you park yourself at the fountain and just keep fishing, fishing, and fishing until the RNG gods smile upon you and you've gotten all 53 coins. Happily enough, the gold coins -- once flipped back into the fountain -- grant you a two-minute buff called "Lucky" increasing your chance to fish up all coins. That said, it doesn't increase your chance to fish up the remaining ones you still need, and because this is a magic fountain, it has the power to duplicate the coins you'll get (a power, I must say, it seems to exercise with great enthusiasm). Just grit your teeth and keep fishing -- and, if you're me, set aside Jaina Proudmoore's coin to carry in your packs while your guild thrashes Arthas, because you are a geek.
For all your troubles, Jepetto Joybuzz (the toymaker in Dalaran) will mail you a Titanium Seal of Dalaran, highly useful for all your coin-tossing needs.