Guild Wars is not free to buy, but it does not have a subscription, and as far as I know there are no micro-transactions. It's a pretty good game. I liked it well enough.
But, you may as well for Guild Wars 2, which is coming soon. It will be the same in that regard, no subscriptions, just the cost of the game, which was pretty much standard price for a PC game when I got GW1.
There are, of course the expansion packs. I guess you can kind of consider them to be a form of micro transaction, but they released a ton of content to the original game for free, and the expansion packs are a hell of a lot cheaper than a subscription.
To expand on this, first I highly recommend GW and secondly there are the following things you can buy after purchasing the game:
1.New Campaigns, there are three guild wars campaigns, Prophecys Factions and Nightfall each one works as a stand alone game in its own right or you can buy more and add them to your account allowing you to travel between them
2. The expansion pack, this requires you to own at least one campaign and it is mainly high area, although it doesn't add quite as much as the campaigns it is cheaper I think and well worth it.
3. Character slots. Ok brief tangent here, GW doesn't have servers like most mmos rather each area is an instance, outside of towns and cities you will have your own personal instance and in a town you will share the instance with other people, once a town instance starts getting full it will spawn a new one. So unlike a lot of MMOs where you are limited to a certain number of characters per server in GW you are limited to a certain number overall, this is 4 for the first campaign you buy and 2 for each of the other two. This isn't very many so you can buy slots for a couple of pounds to add another character. I don't think there is a limit to the number you can buy.
4. PVP campaigns, you can buy a PVP version of a campaign which wont allow you to play through any of the PVE area for it, rather it will instead unlock all the skills for you and let you create characters from that campaign for use in PVP only. These always seemed kind of pointless to me.