We did all this last year (we were at All Star Movies) as neither of us wanted to drive, so here goes:
SEA WORLD
Sea World was pretty easy, I asked a guy at the TTC and he gave me a schedule and told me to get on the Lynx bus and that stops right opposite Sea World. We ended up doing this trip twice, once for SeaWorld and once for Discover Cove. (see below)
Here is a link to the timetable/route map - You want bus number 50:
http://www.golynx.com/routes.cfm
You just need to cross the road and walk through SeaWorld's car park. Really easy and it was only about $1.50 a trip. I don't think we could buy a return for some reason so I think we had to buy a single each time we rode.
DISCOVERY COVE
Close to SeaWorld's entrance there is a free courtesy phone to Discovery Cove, you just call them up and someone brings a car round to collect you (free), takes like 5 minutes. When you're done they take you back to Sea World's entrance (as we were passing the bus stop we asked if we could just jump out there to save walking back through the car park again!!)
UNIVERSAL STUDIOS / ISLANDS OF ADVENTURE
Ok, so we cheated, at our Virgin Holidays rep meeting on our first day we bought some Orlando transfer vouchers. These basically ended up being prepaid vouchers for Mears which you could use for any main park/attraction in the Orlando area. We had to ring up the night before to arrange a pickup time in the morning, and then ring from the parks when we wanted to leave, and they would arrange a time about an hour later to take you home.
So, I'm guessing (not sure) that Virgin will have made money on this, so next time we will probably do this again, but just ring Mears directly. I think it was about $7 each one way. You may be able to pre-purchase these in the UK, but I'm not definite about that.
If you're feeling adventurous, it appears from maps we saw that you can do it by bus if you do the TTC-SeaWorld route with Lynx again. At the SeaWorld bus stop you can then take the I-Ride trolley (this is cheap I believe, about 50 cents a journey) up to Universal. I'm not sure if there is a direct trolley or if you would need to change somewhere though. I'm sure if you search the I-Ride Trolley website you would be able to figure this out.
Personally I'm glad we opted for a transfer here, as it would have been a bit of a faff using different buses etc. They were probably better value here also, with Universal being further away.
We could have used the vouchers for SW and DC, and this could still be a plan if you don't want the hassle of waiting for public transportation, and having to first get to SeaWorld and then wait for Discovery Cove to collect you.
But the SeaWorld bus is really easy, it's only about 3 or 4 stops from the TTC and definitely you're cheapest way.
Hope this has been helpful, if you need any further explanation just let me know, I know I waffle a bit!! :animwink: