Just some thoughts on beginning coin magic - based on me messing around with stuff for a while, and finding out what works for me. I have fairly big hands btw, so that probably affects my opinions on sizes etc.
Bobo's Modern coin magic is always given as the standard reference book for coin workers, and is pretty much essential as a reference, but for actually learning techniques, I have found videos to be much clearer and faster modern alternative. Lots of good stuff available, but for beginner, Michael Ammar's Coin Magic is excellent, and for slightly more advanced/complex material, Sankey's Revolutionary coin magic has a lot to offer. Worth checking out is the Bobo community project, which looks like it will make learning from Bobo considerably easier as the reference videos continue to expand.
Types of coins to use:
A lot of routines have been developed for use with US coins. Many excellent non-US magicians seem to use US coins, but if you're one of the stroppy people like me, who prefer to use UK coins, then this info might help.
10p pieces:
When routines call for US quarter dollars, you can fairly safely use UK 10p pieces, they are nearly identical size (10p coins are slightly larger diameter, and slightly thicker). They are generally similar for concealments and vanishes.
Various aardvarks are available for this coin, including Butter coin, ES, and flippers.
Interestingly, a large percentage of 10p pieces seem to have been minted in 1992, and while these are gradually being replaced or topped up with newer coins, when you see an older 10p, you're on a good chance that it's going to be a 1992, this could be a useful mini mentalism addition to a trick, and it also means that when you're getting aardvarks, you may be better off requesting 1992 coins if possible, so that you can easily get a matching set - some tricks need relatively large numbers of coins (Michael Ammar does a nice simple routine with 8 coins). It's as well to have a matching set handy if you aren't planning on borrowing.
One other thing to note with the 10p piece, is that some of the older ones seem to have a different edge profile, which can significantly affect handling if you have sweaty hands
. It doesn't seem to be wear and tear related, and isn't specific to any years, but generally avoid the ones with curved edge profile (_____) , in favour of the square edged variants [_____] - the curved edge ones have a much shallower milling on the edges which seems to make them slip out more easily 
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Nit picky, yes - but if you're getting a set together specifically for magic, you may as well get the best and easiest to work with.
£2 coin:
Can be swapped in when a routine calls for a half dollar. The sizes are not exact, but they palm quite well. The silver coloured centre flashes quite well for retention vanishes and the like.
Disadvantages are that there are limited aardvarks available for the £2. I have only seen an ES available, and aardvark makers I have enquired wirth seemed to think that making custom stuff with the £2 would be difficult (and therefore I assume rather expensive).
50p coin
Again, can be swapped in for half dollars, if you can live with the non milled edges, and freaky shape (I mean why 7 sides ferpetesake?). Bitten ardvarks are available
2p coin
Could be swapped in for half dollars. Not too bad for palming, despite smooth edges. Limited aardvarks (if any?)
£1 coin
Bit silly for general coin work IMO, but there are a few good aardvarks...
relatively difficult to get any kind of matching sets, as they seem to tarnish in unpredictable way, and there have been so many different designs over the years.
£5 coin
This is a goodie. It's about the size of a US dollar (maybe a bit bigger), and is surprisingly easy to palm with it's well milled edges - despite the considerable weight. You may need larger hands to work easily with these, but the sheer size means a bit of a surprise when you produce them. I wouldn't like to try to palm more than one of these at a time though, because of the weight, and they have a slight tendency to be noisy.
No aardvarks generally available as far as I know, and being not generally circulated, they aren't instantly recognisable, but given their weight, impressive size, and detail (Queen's head etc), they are clearly 100% genuine UK coins when people examine them. (and did I mention, they are huge!
The Royal Mint issue a set of these every now and then, and they are available from coin collectors shops etc, or from royalmint.com at face value.
Small coins (5p/1p/20p)
Generally worth avoiding for people with large hands I reckon. They're more difficult to work with, have non milled edges, and aren't visually very impressive. Limited aardvark potential
Euros:
Lots of aardvarks available, and some good sized coins too, but I haven't used them much, as they aren't so relevant in the UK... yet
. I just want to stress how great retention vanishes and sleeving are. These both loose apeal to many begining coin magicians, but they are great. Don't think an effect where only one hand is shown empty is any good? Work on your presentation and you will devistate the audience. Plus, there are sleights that you can use to show both hands empty. And for sleeving, give it a try. I used to ignore anything that involved sleeving, but now, sleeving is the basis of many of my effects. Sleeving is just as much of a skill as palming and is one of the most versitile sleights you can do with coins. What is the best and safest way to make a coin vanish? Get rid of it! Be sure to give the chapters on sleeving and vanishes a good look-over!
