I need a router for internet access. I have a 50 Mbit symmetrical channel which may be expanded to 100 Mbits in the future. My ISP requires L2TP connection that puts higher load on the router.
I also have a second ISP connection at 10 Mbit which I should be able to use as failover using the router.
My network consists of about 5 PCs used for web surfing, P2P applications like Bittorent, a small Web server, IPTV and on.

The router should have 2 WAN ports, 2 LAN ports (one for for IPTV) and wireless. Gigabit ethernet is preferred.
The desired throughput for the router in L2TP is 100 Mbits to each side not to experience any slowdowns.

Which hardware suits my needs better ?

I recommend you to visit http://routerboard.com
You can see RB751U-2HnD and RB750GL
The first have what ever you want but doesn't have Gigabit port.
The second have Gigabit port, but doesn't have Wireless interface.
These two are the cost effective solution by Mikrotik. If you want more than these, RB1100AH is a good solution. Then you may need to buy a simple Access Point.

Thanks for your reply. I visited the products page first of all.
I'm afraid that RB750GL can be too slow for my purposes and my budget is higher.
RB1000AH may seem a good solution. But is that level of performance an overkill ?
Can I consider something in between ?
Is RB493G enough for the needs stated above ?
Or should I choose RB800 ?

Really I don't have this experience like your network to see whether which RB works well for me or not but I think RB493G is enough if you don't have any problem with it's level 5 license.
BTW, if I were you and have no problem with budget, I will buy the RB1100AH although I have 2 RB1100 now in two different network and they work well for me.