There are lots of them, but you don't want to pay too much for them. Eck or Joey Devine would probably be the best if money is no object. Niggeling, Northrop, Mike Adams, Neftali Feliz, maybe Gagne if you're feeling lucky.
The key is to match their cost to their role. And the obvious answer to how many innings you need in your 'pen is the total # of innings you need minus the total # of innings you're getting from your starters.
I always try to get a closer in the 40-50 inning range. I only want them pitching in save situations and any more might be wasted.
And I always try to get a Long A guy who can give me 2-3 innings in a game if my starter gets killed. Typically that will be someone in the 90-110 inning range with at least 3 IP/G.
Then I fill in the rest with a mix of setup A and setup B to get me to the innings total I need. I guess the split would be about 50-50 or 60-40 in favor of SetupA guys. Remember, you don't want a lights-out guy pitching when you're down 3. You could use that money somewhere else.
If it's a higher cap league or I need a bunch of innings then I'll add a Long B as well, who would be worse than the Long A guy.
I typically use ERC# as the key stat for my pitchers. So let's say that my starters 'average ERC# is around 2.50. Then my staff would look something like this:
Starters 2.50erc#
Long A would be around 3.00erc#
SetupA would be around 2.00erc#
SetupB would be around 2.50erc#
Closer would be around 1.75erc#
LongB (if needed) would be around 3.50-4.00erc#
Yes, I know that sometimes having your closer as your best RP when you have a 3-run lead in the bottom of the 9th isn't the best situation. But on average, a closer faces the highest leverage situations, so you just have to hope for the best.
Also, remember that if you have AAA then you want to leave space for them on your 25-man roster. So if you have 6/2 AAA like in an OL then you are drafting 17 "real" players and 8 200k guys. So if you draft 8 hitters and 9 pitchers, you have to be sure you get your innings from just 9 pitchers.
If you're in an OL, you can count on your AAA guys for some long B work if you're lucky. I wouldn't count on more than that. They tend to be terrible.