I have a 6' Scheels medium spinning rod with a Pflueger President 6930X reel. I just bought a Fenwick Aetos 6'8 MHF casting rod (got an awesome deal on it). What kind of reel should I get for this rod? I am also thinking about getting a third rod. What kind of rod/reel combo should I be looking for to complete my arsenal? Also, if someone could explain what techniques I would use each of these three rods for that would be awesome.

For the aetos go on ebay and get a lews lfs speed spool for 80 dollars 

For a third rod get a medium power moderate action casting rod with a low gear ratio reel spooled with 10lb fluorocarbon 

The spinning combo will be for finesse techniques. The medium heavy will be for jigs, worms, s pinnerbaits, Texas rigs. If you get a third rod u would use a moderate action rod for crankbaits.  I would also consider adding a medium power extra fast action casting rod for topwater and jerkbaits

A few suggestions here. 

Next rod depends on what lures you plan on fishing, what weight and what kind of cover you will be fishing in.  Any of the lighter lures should work on the spinning rod including crankbaits.  The Aetos will work for any single hook presentation.  BTW, you got a nice rod.  It is a bit shorter than many like for bottom contact lures, but will still work.

What is your budget for the casting reel?  A Tatula can be had for about $100.  A Lew's Tournament MB for $109.  TW has the Zillion TWS on sale for $200.  Amazon has the Okuma Helios Air for $159 (TW sells for $250, but I think list is $270).  This is a great deal.  Was impressed with mine enough to get a second one first chance I got.  Maybe a Pinnacle Optimus LTE.  Pinnacle seldom gets mentioned, but I liked my first one (a Primmus) so much I jumped on two more when they were on sale at manventureoutpost.  There is a Primmus Shoreline on ebay for $130.  Different finish than the Primmus Xi (selling for $225 ot TW) and may not be hand tuned at the factory like the Xi.  The Primmus and Helios Air weigh less than 6 oz.  The Shoreline weighs 6.7 oz. and has wood knobs.

A reel with a ratio in the 6s is considered good for an all-around reel.  Most people prefer a faster ratio for bottom contact.  I'm getting so I like a fast ratio period, but that may be a fad I am going through. 

I like the suggestion of a M-XF.  FFO has the Fenwick Elite Tech Smallmouth 6'9" M-XF  for $74.88.  These are fantastic rods at the full $130 price.  I'd rather have this or a MF for my next rod than a crankbait rod.  The spinning rod should be able to handle crankbaits just fine until you decide to add a couple more rods to your arsenal.

FFO also has another Smallmouth rod I really enjoy using...the 6'10" MH-MF....same price.

1 hour ago, lakeannaangler said:

For the aetos go on ebay and get a lews lfs speed spool for 80 dollars 

For a third rod get a medium power moderate action casting rod with a low gear ratio reel spooled with 10lb fluorocarbon 

A good reel, but I would spend a little more and get the Lew's Speed Spool Tournament. It's much better than the basic Speed Spool

15 minutes ago, briansnat said:

A good reel, but I would spend a little more and get the Lew's Speed Spool Tournament. It's much better than the basic Speed Spool

Are You talking about the tournament Mb. What makes it better Than the basic speed Spool

16 hours ago, beginningfisherman said:

I have a 6' Scheels medium spinning rod with a Pflueger President 6930X reel. I just bought a Fenwick Aetos 6'8 MHF casting rod (got an awesome deal on it). What kind of reel should I get for this rod? I am also thinking about getting a third rod. What kind of rod/reel combo should I be looking for to complete my arsenal? Also, if someone could explain what techniques I would use each of these three rods for that would be awesome.

For me it would come down to to the type of fishing I planned on doing. Maybe medium or medium heavy/moderate action rod would be a good addition to fish crankbaits. Also l, a seven and a half foot heavy action rod would be a great addition of you plan on flipping or frog fishing in heavy cover. 

As far as the reel goes, I would get something in the 6:3:1 gear ratio range. I'm partial to shimano and lews but this is a personal preference. There are so many great reels out there that it would be hard to give a recommendation without knowing what you'd like to spend.