Not sure if this thread is re. ODIs or tests, but here goes anyway.
ODIs: Australia. They will lose McGrath (and that is huge of course) but will have one or more of S Clark, Hilfenhaus or Johnson to come in. Look for Doug Bollinger as a smokey in ODIs here as well.
Tests: harder to tell, frankly.
Pakistan seem in a state of flux, not sure who will be bowling for them if Akthar doesn't aim up.
Likewise England because of injury/ lack of mints (that was for you Rich!!
). If they get Jones & Flintoff back they will be pretty potent, especially if someone takes Harmison to the continent and dunks his head in the water at Lourdes to solve that conundrum. Monty looks like he'll be a reall asset to them for many years as well.
SA's attack is still pretty good, but is there some younger quality in bowling coming through? Don't profess to follow their domestic stuff that closely so hard for me to say, but is there a ready-made replacement for an aging Pollock?
India's pace stocks don't look that great atm, though their spin ranks are still good.
Sri Lanka, with at least 2 more years of Murali, Vaas still solid and Malinga on the rise look pretty good for the medium term imo, although Chaminda is starting to get on a bit.
NZ rely so heavily on Bond - if he's not there, hard to see them bowling sides out twice on a consistent basis. Vettori is good, but I don't know if he will take enough wickets consistently to get them over the line.
I'm going to throw a wild card in here and I'll probably be laughed at, but I think WI have the potential to have a reasonable attack in coming years, if Taylor and Powell kick on. Having watched the 1st test this week, I know they didn't bowl well on day 1, but they'd had hardly any cricket, and Powell in particular was pretty unlucky and looked like he got a fair bit out of the conditions. Their 3rd seamer isn't as good as others, and they lack a spinner (Dave Mohammed aside) but it would be very good for cricket if those 2 young blokes really kicked on as a new ball force. It would at least give them a base with which to be more competitive.
Which leaves Australia - McGrath & Warne gone and they cannot be replaced. Clark will do a McGrath to some extent, Lee will be there (can be expensive), and then there's a choice of Tait (fast but erratic atm), Johnson (untried but offers left arm variety), Hilfenhaus (swings it around a bit) and Dizzy (tried and true, but maybe not what he was). I think they might run with Tait for the home Tests here, but would not be surprised if Hilfenhaus got a game at some point. As for spinners, McGill is obvious, but won't be around for too long, likewise Hogg. Which leaves Bailey, Cullen, Hauritz, White et al, who haven't really shown that they are up to it yet. Then again, neither did Warne before he was picked, and he went ok, didn't he.
In the medium term, I think SL will have a good attack, which has the arguably the best balance.
Pakistan and England next, injuries and unavailabilities aside, with Australia a bit of an unknown quantity, though potentially still very good.