There is a very useful point conversion calculator at WebFlyer here. It shows how you can convert from one award partner to another. It also lists options for how to top up a specific account.
You should also keep your eyes open for limited time deals and promotions e.g. American Express are currently offering (until May 31st) a 50% bonus on Amex Membership Reward Points transferred to British Airways Avios points. As I mentioned here I have signed up for numerous credit card sign-up bonuses including the 180,000 MR points I earned from applying for 2 AMEX credit cards, so today I availed of the transfer bonus into 270,000 Avios points which posted instantly. I had already got the bonus of 100,000 Avios points from signing up for a British Airways Visa credit card so now I have 370,000 Avios points for future trips by simply opening 3 credit cards. Not bad for a few minutes work. Let me know of any good transfer promos you know of.
Check out the rest of my travel hacking tips here.