I'm totally stealing borrowing this from another thread where ArchPhantom (I believe it was him) posted a sand team -- Seismitoad seems like a really solid teammate on sand as it boasts an immunity to water and doesn't take residual damage from the sandstorm. As mentioned before water weakness is a huge problem for sand teams as the main abusers are weak to it and this makes rain teams a serious threat, so any immunity to water is huge. It also makes a good Stealth Rock user if you opt for Scarf with your TTar (although Smooth Rock is often preferred to help Excadrill out).
Also as a water resist I like Ferrothorn, but I'd recommend pairing it with Hippowdon more than Tyranitar because of a shared weakness to fighting that Excadrill also shares. I do think more teams tend to use Tyranitar because of its offensive presence and ability to get rid of Psychics/Gengar, but there's something to be said for using Hippowdon. Bulkier sand teams can wear down opposing teams thanks to residual sandstorm damage, and this is especially helpful against Megas like Lopunny or Charizard X both of whom Hippowdon checks.
Since rain teams are a serious threat, I'd say any sand team needs an answer for Swampert. Rotom-W is great since it can Will-O-Wisp Swamp while resisting both of its STABs. Defensive Rotom-W is also great for Keldeo since Secret Sword hits physical defense. Another fun thing to do is run Zard Y since it helps alleviate pressure from rain giving you a 2nd weather inducer while also weakening water moves. Although it is not really a sand mon it has pretty good synergy with the playstyle since it allows you to break down common walls to Excadrill such as Skarmory.
EDIT: Latis are also solid teammates with immunity to ground and resistance to water, the ability to nuke physically defensive pokemon that check Excadrill and adding Defog support so that Excadrill can go full offensive. Latias also provides Healing Wish support for a 2nd opportunity to sweep
All in all I think sand is the most versatile weather since it gives both offensive boosts (Sand Rush) and defensive buffs (Rock type SpDef), while having 2 different weather setters that are solid pokemon in their own right even without Sand Stream.
Also as a water resist I like Ferrothorn, but I'd recommend pairing it with Hippowdon more than Tyranitar because of a shared weakness to fighting that Excadrill also shares. I do think more teams tend to use Tyranitar because of its offensive presence and ability to get rid of Psychics/Gengar, but there's something to be said for using Hippowdon. Bulkier sand teams can wear down opposing teams thanks to residual sandstorm damage, and this is especially helpful against Megas like Lopunny or Charizard X both of whom Hippowdon checks.
Since rain teams are a serious threat, I'd say any sand team needs an answer for Swampert. Rotom-W is great since it can Will-O-Wisp Swamp while resisting both of its STABs. Defensive Rotom-W is also great for Keldeo since Secret Sword hits physical defense. Another fun thing to do is run Zard Y since it helps alleviate pressure from rain giving you a 2nd weather inducer while also weakening water moves. Although it is not really a sand mon it has pretty good synergy with the playstyle since it allows you to break down common walls to Excadrill such as Skarmory.
EDIT: Latis are also solid teammates with immunity to ground and resistance to water, the ability to nuke physically defensive pokemon that check Excadrill and adding Defog support so that Excadrill can go full offensive. Latias also provides Healing Wish support for a 2nd opportunity to sweep
All in all I think sand is the most versatile weather since it gives both offensive boosts (Sand Rush) and defensive buffs (Rock type SpDef), while having 2 different weather setters that are solid pokemon in their own right even without Sand Stream.