Basically i'm looking at getting a new anal toy and i really do want a realistic penis dildo but have 2 questions before i go ahead with getting something.
1. I already have a standard butt plug and a curved booty buddy which i love so would there be any real difference in sensation with a realistic penis dildo compared to those or is it pretty much the same?
2. I've looked at anal dildo's like the Doc Johnson Crystal Jellies but would it be fine to just get any dildo as long as it's sized right and nothing huge?
There definitely is a difference between a plug and a dildo. I like butt plugs (I have quite a few in varying sizes!) but I love the feel of a dildo thrusting in and out.
My favourite is the 8" Lovehoney one:
http://www.lovehoney.co.uk/product.cfm?p=22815
Another favourite, which I don't use quite as often (because it's bigger) is this, which feels really awesome (VERY realistic):
http://www.lovehoney.co.uk/product.cfm?p=10747
If you're still relatively new to anal then you probably won't be ready for that second one yet, but the 8" Lovehoney one is really good (AND it's in the sale at the moment!  )
The important thing when choosing a dildo to use anally is to make sure that it can't... get lost. Whether this is because it has a flared base or balls or whatever (balls are my preference).
I'd also advise to get one with a suction cup as this means you can ride it hands-free, which gives you a lot more possibilities 
Whatever you choose to get, enjoy!
Thankls for the response
I'm not new to anal but only been doing it properly with these two toys since last year.
Lovehoney BASICS Slimline Butt Buddy Butt Plug
http://www.lovehoney.co.uk/product.cfm?p=16053
Lovehoney Booty Buddy Silicone Butt Plug
http://www.lovehoney.co.uk/product.cfm?p=16665
I of course realise i need something that won't get lost and have thought about something with balls for added realism. Also since my bathroom is now tiled it makes it perfect for something with a suction cup