I pay AOL £29.99 for unlimited usage 8meg connection. I also pay them just £5 per month for unlimited 24/7 local AND national phone calls across all the UK, which is what BT charge just for offpeak. International calls are also very cheap, 2pence for America (either mobile or landline) 3 pence for Australia etc...
I know others diss AOL,(it is usually those who have never used the service, but rely on heresay) but I spent 5 years being a reporter for UK ISPs every day. I can tell you that AOL are the only ISP who have never gone back on their word, and have never imposed any restriction, and provided exactly what they advertise.
I have had a reliable ongoing connection for 9 years and when they dropped the software a few years ago, it was even better. However, they are in talks to sell their UK counterpart, and carphone warehouse are rumoured to be in line for it (the talk talk people) and if they get it, I will find another ISP sharpish.
Their CS is not as good as it used to be since they outsourced to India, although I think I have rang them 3 times in nine years, and two of those times was to put my free upgrade in speed forward. However, if you are looking for good CS support with the Mac, then AOL is not for you.
Talk talk are a nightmare whether you use Windows or Mac, and Toucan also have many horror stories.
Do you use a router at all? If you do, I can't see where you will need any ISPs customer support much unless you are having issues connecting.
NTL support the Mac and will usually set it up for you, and Demon also support the Mac, but Demon's once excellent service has deteriorated in the last 12 months.
Virgin also offer support for the Mac too. I know NTL is unlimited now, not sure about Demon or Virgin so better to check them out. Bulldog have recently been sold to Pipex, as have Toucan. Pipex gets mixed reviews, and I know they have restrictions and a FUP too, so if you do a lot of downloading, they may not be the answer.
Bulldog also had mixed reviews, and many reported recieving a poor service just before they were taken over with Pipex.
I would ring around a few who say they support the Mac, and see what their general tone is over the phone, and you may gather more that way
I know IDnet (again restrictions) are meant to be very good, as are Zen, although I am unsure whether these support Mac's or not.
If I was in your position (and I may well soon be with AOL selling), I would go either NTL or Be* - but Be* are an LLU provider and they need to be actived at your exchange.