I went to Sri Lanka to ordain a few years back, but failed to find a suitable place for what I wanted to do, I spent ~2 months at Nissarana Vanaya - Meetirigala under the Venerable Dhammajiva Thero. He speaks fantastic English and the monastery is fantastic, very well funded by Sri Lankan standards. The monks there keep very good Vinaya by and large and as a part of the Galduwa tradition (Sri Lankan forest tradition) it has a good reputation amongst the pious Sri Lankan laity.
Ven. Dhammajiva will give you a meditation subject in line with your prior experience - For instance if you've already been practicing anapana he will continue to help you foster that, if you've been working with rise and fall of the chest he'll help you with that (that seems to be the preferred method there - As Ven. Dhammajiva spent many years in Burma under Ven. U Pandita if I recall correctly.
Personally I am trying to get rid of my debt so I can find a suitable place to ordain again in the next few years and if I chose Sri Lanka I would be more inclined to try and nag the hell out of Ven. Nyanananda 'till he relents and ordains me, as a Venerable monk of the Thai tradition told me he doesn't usually ordain people but if I rocked up and explained my situation (that I don't want a traditional mahavihara teacher) and nagged him enough he probably would.
So it depends really on what your practice involves. At the time in Sri Lanka I grew quite disconcerted by the fact that every Dhamma talk seemed to return at some point to the doctrine of flux - One that I think is logically and fundamentally opposed to the Buddha's teachings, but for one who does not have such qualms I think Meetirigala could be a good gig.
I also went and stayed at Kanduboda, not the old one but the new one under Ven. Pemasiri. Ven. Pemasiri is quite famous in Sri Lanka and his centre is very well funded and the conditions are excellent. It's not in the forest though so you do have to put up with some occasional noises such as tooting horns and the Muslims with their loud speakers blasting the call to prayer and various music through out the village at times in the evening. There's a lot, and I mean ALOT of westerners at Kanduboda, which can be a massive relief for those who start getting culture shock. I got a bit of that at Meetirigala because with my internal strife my meditation wasn't going well, so I began to lament the fact that nobody besides the teacher spoke English and I was very lonely. At Kanduboda there were a lot of people I could talk to. There was even a New Zealand monk there so I could relate kiwi stories with him, the only problem I found with the place is that the vinaya wasn't up to par for my wishes, I have no intentions of divisive speech so I'll leave it at that.
There are a lot of pious sinhalese lay people, and they bemoan the fact there aren't more good monks, there is a lot of sangha corruption in sri lanka which the laity are all too aware of. But they are also aware that the Buddha spoke prophetically of this age of degradation and said that even when the Sangha was filled with immoral monks who didn't practice his teachings that a gift to the Sangha was still of immeasurable value - So many sinhalese are very generous with their dana. Be careful not to take up any offers of people to be your dayaka unless you're absolutely sure you'll be staying in the robes. I did this by accident as much as by simple ignorance and I ended up upsetting an entire extended family who refuse to speak to me now because in their eyes all their hard earned gifts they gave to me (just things like food, mosquito repellent, a clock etc) were worthless when I stopped being an anagarika and returned to the lay life.
But if you do choose to become a monk, this can work very much in your favour as you will have absolutely no problem obtaining any requisites you need for the holy life, and quite possibly some things you don't
need, which can then be passed on to the Sangha at large. It can cause issues though because other monks can become jealous of the rich Suddha who has all these dayakas tending to his every need, especially because you will be newly ordained or even just an anagarika (as I was) and you will have all these people wanting to help you (it can actually be a hinderance to one's practice) - So my advice in such a situation would be to share anything you don't desperately need with the community and that way any immoral monks will see you as a benefit to them rather than a thorn in their side. Not to put you off, but there are a lot of scurously monks out there (although the Galduwa has a lot less of such monks) I heard stories from Western monks while there of incidents of suddha monks being poisoned or threatened in one case death threats to leave town, because the local temple felt the western monk with his actual precept keeping and meditation would result in less spoils of dana for them. So in your travels just be careful not to piss anyone off haha, work that metta meditation to the max and try not to step on any toes, always always be humble, Sri Lanka like other Asian nations (although less so) has a culture of non-confrontation, criticisms are made indirectly - Especially in the Sangha, so do not speak harshly or criticically of anyone or their ideas to their face, find ways to suggest alternatives in manners that do not insult a person's precious sense of pride or 'face'.
Ultimately it's a case of having realistic expectations of what you're going to find. As Rob points out in his post above. You will find most monks are just average human beings, like all of us they are affected by greed, hatred and delusion, and while some are working hard on cutting those roots off, many others are not. Those who are of such a high calibre of bhavana are usually tucked away in remote areas such as Laggala (which I had the pleasure of visiting), so you'll do best if you don't go in thinking it's going to be like it is in the Suttas.
Anyway that'll do for now, if there's anything else you want to know just ask