I'll open this brief post with the caveat which always applies when considering future major league relievers - a lot of them are minor league starters. One need look no further than Chad Jenkins. His odds of being a productive long term major league pitcher are substantially higher in the bullpen than in the rotation. Among those who've already appeared on the starter lists, it's easy to identify pitchers who may end up making their career as a reliever.
Marcus Stroman, for instance, is often cited as a guy who could pitch in the majors from opening day if it was in relief. John Stilson is said to have electric stuff, but also health and mechanical issues that lead some scouts to suppose his future is late-inning relief. Sean Nolin may simply be pushed to that role because of the depth of the rotation options and the value of a quality lefty reliever (which is the one pitching related "position" in which the upper level depth is too thin, if Oliver retires. It's not practical to list guys who've been mentioned before on more than one list, but I'll make one exception.
1. Sam Dyson (5/7/88) - Ihave to admit I'm basing this report on the exceedingly high praise of scouting reports. Dyson is a high groundball-rate pitcher who's ratios do not really reflect the talent that had John Farrell calling him one of the best arms in the system. Dismiss Farrell if you want, but the Jays would not have promoted him mid-season and thus force themselves to protect him on the 40 man roster this off-season if there wasn't something to the praise.
2. Chad Jenkins (12/22/87) - This ranking is based heavily on proximity to a major league job as compared to those who follow. I'm not really high on him, but the closer you are to the majors, the less that can go so significantly wrong that you don't make it. I expect him to pitch in the Buffalo rotation out of ST ad while a spot start can't be ruled out, if he stays Blue jays property, he's almost certainly going to do so as a reliever if he's in the majors at all.
3. Dan Barnes (10/21/89) - On the other hand, if you are looking at pure results then it's hard to not think very highly indeed of Danny Barnes. It would be pretty irrational to ask more from a minor league reliever than Barnes has already delivered. In over 156 minor league innings, the 6'1 RHP has a masterful 2.13 ERA and 12.5 K:9 (as compared to 2.9 BB:9). He has yet to be significantly challenged and he should open the season in New Hampshire. It's not at all impossible that he could pass both Dyson and Jenkins this year by the time the jays have need to call on one of them.
4. Evan Crawford (9/2/86)- No less an evaluator than Alex Anthopoulos spoke in growing terms.about Crawford last spring. He'd opened everyone's eyes with a great campaign at New Hampshire in 2011 and impressive work in the AFL. But this year went quite poorly, both in his major league opportunity and upon his return to the minors (Las Vegas caveat applies). The hill is a bit steeper to climb now, with Cecil in the pen, Happ squeezed out of the rotation, and Aaron Loup staking his claim last year (and don't forget that Luis Perez will be back sometime in the second half if there's no setback). but I'll give him one mulligan and be watching to see if he regains his form in Buffalo.
5. Matt Wright (5/7/87) -Wright is, statistically, following in the footsteps of Crawford and Loup.He's a LHP and his rations have been good to great all through the system. He's been a tic old for the level in most seasons but still, on paper he should be something to get excited about - yet I was stunned as no one took him in the Rule 5 draft. So maybe the scouts know something I don't.
6. Griffin Murphy (6/7/92) - my one exception, he DID spend pretty much all of 2012 pitching in relief. but he seems a sort of high profile guy to be so quickly moved out of the starting role and so i'll wait and see how it goes in 2013.
7. Alan Farina (8/9/86) - After 2010, it seemed Farina had re-invented himself in relief and climbed into the prospect radar. He'd put a miserable 2009 (also spent in relief, to be clear) behind him and was on his was. He opened 2011 with 17 effective innings - and then was disabled and on his way to TJ surgery. Results were mixed upon his return last year, but there may be something there in his second year post-surgery. however, at his age he needs to be challenged so Buffalo, or at least New Hampshire, will have to be the scene of any success worth being impressed with.
Coming soon, my (radically altered) combined top prospect list.