It's difficult to make specific recommendations given that audio device manufacturers update hardware and drivers on a regular basis and your needs will be very different to the next person. This FAQ considers some important issues to consider in your search for a sound-card.
Note about audio quality: The only time your sound card or audio interface can influence the quality of your rendered tracks, is if you have used recordings or samples made with it in your track. Otherwise, your audio device just playing back digital audio data that has been processed by FL Studio.
Get ASIO! Of almost equal importance to your CPU speed is that your soundcard / audio interface supports ASIO drivers. ASIO is a software device driver standard that allows FL Studio direct access to the soundcard rather than communicating via the Windows operating system (as with the standard Windows driver). This will mean a significant performance advantage when running FL Studio. Look for a sound card for which the manufacturer has written custom ASIO drivers (check the specifications for mention of ASIO or ASIO2 support). NOTES: ASIO is all about software to hardware communication efficiency and performance here has little to do with the capabilities of the underlying hardware. FL Studio ASIO provides the full flexibility of ASIO for almost any device you are using, but it is not as efficient and low-latency as a native ASIO driver written for a specific audio interface.
These days, the onboard sound from laptops and motherboards is usually very good. However, we can probably do quite a bit better than that in terms of CPU efficiency and 'somewhat' better in terms of audio quality. If you are not recording external instruments / vocals (where you should buy a dedicated audio-production audio interface, see below), we suggest the Audigy RX or Sound Blaster Z ~ $70 - $100. You may be surprised we are recommending a consumer soundcard, however the ASIO drivers are excellent (including the very, very useful record 'What U hear' option). The Z has very wide compatibility with Windows XP through to Windows 10 64 bit, plays nicely with the widest variety of software applications AND the A/D & D/A converters in it are excellent. Really, the only downsides are the robustness of the connectors and lack of professional connection standards like XLR and balanced line-in. If you don't know what they are, then you probably don't need them.
I want to record audio and or want to use professional monitor speakers: